Downgrade spikes?
I ended up just farming up the 3 star gun, which was mainly annoying because I had to spend a significant amount in t1 and t2, where half the time in t1 was just wasted running through s1 anyways to get to s2 because I didn't need the spikes from s1.
It really just doesn't make sense to make vanguards play T1 arcade, especially not making an incentive to just run past the first stratum. That's just bad design.
T2 is not preferable, but it's at least ok profits, but I have way more fun just playing content at my progression level, ie, t3. Overall, I would much rather have just played t3 primarily, with maybe some t2 for a change of pace, instead of spending most of the time actually making progress in just t2 since I didn't grind all that much, and wanted to achieve something, so I had to work my way up the tiers to get a gun.

So it'd be good if you added some way to downgrade spikes, or making spikes from lower depths drop in higher depths as well. Preferably downgrading, if you want to preserve the ability for lower rank players to farm the event for profit.

Natural-looking gates?
I do appreciate that the gates were forced to have construct stratums so we can at least play the event on any day at full efficiency rather than hoping for stratums that are good when we want to play. That said, I do not appreciate that they broke the existing rules of having each boss always available, and that each depth only had a specific room, nor that every such depth you made was, in the exact same order: No status, Freeze, Poison, Shock. It broke the immersion to have this blatantly handcrafted gate, and it's honestly baffling that you didn't realise you made exactly 0 fire themed floors.

So it'd be good if you make some system that influenced the gates to make construct stratums appear so they can be more natural than your handcrafted gates, and to save effort for the future, especially if you intend to make other, similar, events.

Look for bugs please
It's also baffling that you let a fairly major exploit for farming the spikes in, when you had tested it. Did nobody spot it? Or did you rush to implement the event while neglecting feedback? Also just the rush to fix that creating a new bug where retrodes dropped nothing, and, just, the lack of timely communication about what these updates were about when you did make them.

In general, always keep in mind what would be bad if it was possible to exploit, and test it. It would not have taken you guys long to test yourselves if the different spawners spawned spikes.

Playing on Elite should be rewarded
And it hurt the experience that there wasn't much reason to play on Elite if you actually wanted the spikes.

So overall, I honestly really just think it would be good to make rewards scale with difficulty. Even if it's just something simple like a chance for spikes being picked up to count twice on a higher difficulty would have been good. Or alternatively, making spikes appear more often, increasing the challenge even further, would have been fun, though might have been hard for newer players.
And on that note, there should also be some buff to the spikes for being in a Shadow Lair. Because as it stands, I got a very disappointing amount of spikes from playing RRT despite a significant increase in the difficulty.

Material cost ratios
And overall, it's just silly that each recipe for the mandolin requires playing the lower stratum more than the actual stratum its star rank should represent. I can only assume that you did this because you wanted something similar to regular recipes, where the 5 star material you need only 1 of for a 5 star weapon, but you need 20 0 star materials. The difference there, though, is that regular materials drop in higher tiers than their minimum tier, instead of being forced to appear in only one specific stratum, like the spikes.

So, I do believe it would make more sense to have the ratio flipped, where the matching star rank is what you need most of, rather than needing more of the prior star rank material for a given star rank slicer.

That said, I did enjoy the event, despite the hiccups. I just think several of them could have been avoided. I will be looking forward to new content.