Originally I had a much longer reply, but then I remembered I am on the forums and giant blocks of text are too scary. I believe the heart of this issue is the Forge, but there are other reasons to improve the depth/gate generation issues.

For the sake of (what I believe to be, minor) economics, the forge was implemented, which "forces" us to seek out these deeper depths much more than we likely would otherwise. Don't we have biweekly promotions to cover this, is OOO really relying on players using real money to buy energy to get rarities from the depot to level up items to compensate for the loss of elevator pass revenue? The forge seems entirely unnecessary, as it is ultimately a bottleneck to slow players down, especially when you think about the bound state of rarities acquired randomly from exploration. We have plenty of items to consider for heating (*cough gunner cough*), we do not need a forge to limit player progression, which I believe is the core of the issues outlined in this thread. Get it? CORE? DaN? I'm hilarious. Anyway, point is, we're not going to run out of gear to heat anytime soon (some only heat the important things such as chaos/black kat, which is still pointing to no need for the forge, since the bottleneck effect is limited if players only choose to heat a few key items, but where's the fun in no variety?), even if we are able to heat faster without the forge...but...

I have a few ideas about the forge that don't involve its removal - an option to use the old heating system (minus the reviving of course) that temporarily overrides the current system is completely viable, and might help the serious issues heat amplifiers currently have. Who in their right mind would spend that much energy on a temporary amp to fill heat bar(s) per floor, when many of the better heating floors don't even have arsenal stations, requiring reinvites from friends and sacrificing boss tokens?

I think a new usable, perhaps something called a "Heat Lattice" that, when activated, removes the forge system for your knight and you heat the old way, sacrificing a chance for juicy Forge Prize Boxes for a price while saving time could work very well. Just for the duration of the lattice. I use the term "lattice" because I think it fits, it could be a perfected fire crystal (as in crystal lattice) that either decays with time or has a limited number of uses that just bleeds heat radiation into your equipment in an overwhelming manner, purifying the heat you pick up and releasing it when stepping onto an elevator as it syncs with the wonders of the clockworks, resonating with the power of minerals, which I'd love to see returned to the arcade's gate generation in some way. The Heat Lattice used in junction with a more fairly priced heat amp would allow the "collector/completionist" type of gamer to have a fantastic, sill long-lasting Spiral Knights experience. To balance this further, rarities could just not drop from boxes while the lattice is active, feeling overwhelmed by its manifestation of energy and too shy to show up. Lol. I'd also remove the failure chances in the forge, replacing the three buttons with these options: use X crystals to forge, done. Use 2-4X crystals to have a chance at getting a Forge Prize Box or the other benefits such as double leveling etc. Failure is just...sickening. And disrespectful of player effort and time. It's also terrifying to think about misclicking. Ugh.

I agree that gate generation as well as "depth rewards for effort" need work, as the system seems to have been steamrolled by the battle sprite update. Too many things were just left in the dust, and not enough time was spent talking with players about the non-battle sprite changes. Green/blue minerals are currently only used for Geological Survey, the abrupt removal of the ability of players to manipulate the arcade with minerals in junction with free elevators, heat amps remaining pricey, and of course the forge are factors that point to a jerry-rigged system we've dealt with for far too long. While I think moving the depths of vanguard missions to be deeper would be excellent and slightly more challenging, I think allowing us to create things that show up in the arcade, and allow players to manipulate the arcade again, would solve many of these "stagnation and too much grinding" issues. Would you play the arcade to get to a guaranteed arena in D28? Yes. Would you play to see a level you or a friend made randomly show up along the way? Oh I definitely think so! Which brings me to...

Let us make levels in steam workshop. Oh snap, this thread is from OP too! And one that has been suggested in some form time and again. I've even proposed that it involve the artifact (ties into endgame lore), which could easily incorporate minerals now that I think about it, in an interface similar to the Guild Hall design mode. New players spend minerals feeding their sprite(s), then after they understand the intricacies of the game and have reached the more involved vanguard missions, they could use minerals with the artifact to design levels and/or call forth existing ones (reminiscent of the old gate construction) - with other players, we'd surely all agree on the best (arenas, as well as player-created levels approved by staff), resulting in gates we are proud of and happy to play in together.

These are more reasons to play, besides personal gain from drops and heating. Let the desire to create and explore be the drive for us to be in the arcade, not the false "need" to grind. The game is suffering in part because of a horrible grind, despite them advertising no grind. I suppose they can claim that... if the grind is "optional," but come on.

Okay I still made huge blocks of text. I am just passionate about what I believe will make the game much more enjoyable for a huge percentage of the playerbase.

On a side note more related to the specificity of this thread, I think they could get rid of one of the DaN randomly generated levels, especially if they make the whole thing deeper as OP as proposed (which would make sense with the core terminal anyway, don't even get me started on depth issues. *cough* A New Threat *cough* Breaking in the Recruits *cough* Grinchlin Assault *cough* several others. Also, loading into DaN's terminal unlocks the "hardcore" achievement...well, it did. I'm not sure if it still does. Just hilarious. Also, Apocrea is deeper, it's not like there has to be a hard depth limit that's all mysterious like Shadow Lairs). They didn't even bother giving these two levels unique names as they do with other missions, even HoH has floor name variability. This would cut down on grind time too, and be a less...intrusive treatment. Certainly not a cure.

TL;DR: I agree, but feel that there is a "deeper" solution we can reach as a community. Give us dynamic heating options to reduce the grind, and allow us to create our own levels as well as call forth our most favorite areas together (similar to old gate construction), providing more incentives to play than personal gain.

@OP

12 items? Ok yeah I see your pain lol

Minor quibble: Instead of "Levels that should end on..." you should write "Missions that should end on..."

Minor quibble: It Came From Below currently ends with an Unknown Passage level that has no boxes. You want this at depth 28, so that the preceding level is depth 27? Then you propose to "add a handful of boxes". To which level?

Moderate issue: Reasonable players may disagree with your assessments of mission difficulty. Generally, missions get easier the more you run them. In particular, players underestimate the difficulty of FSC because they have done it so many times (and optimized their gear for it). I found my first DaN to be easier than my 100th Vanaduke.

Major issue: Low-paying compounds are a problem at depth 27 and 28, but they're also a problem at depth 15 and depth 21 and everywhere else. The solution is to fix compound payouts. This is both easier and better than trying to force particular levels at particular depths (e.g. arenas at 28).