First off, let me get some bile out of the way. Whoever's in charge? I need you to track down the guy who thought it was a good idea to implement a random chance that your progress would just fail. Fire him. No no, I don't want to hear it. FIRE HIM. "What do you mean you lost your progress, you get to keep your heat on a failed forge!" I could heat this weapon five times over in the time it takes me to re-farm the crystals for even the lowest-rank (AKA: Guaranteed to fail) level of forging. Seriously, you took something that used to be free and painless and made it actively stressful. I understand that, with elevators now free, you need some kind of gating mechanism to keep people from advancing too quickly. Guess what, you already have that! It's called CRAFTING. You either let people farm the orbs (that system has some issues too, but you got the drop rate fairly reasonable on the first try, congratulations on that), or you let them PAY YOU MONEY. I fail to see how this was a bad system. I seriously want to inflict physical harm upon the person who came up with this piece of dreck, but that won't solve anything, that won't help anything. Removing him from the design process will. So fire him.
Moving on.
Despite how provably bad the forge system is at the moment, you're not going to take it out. No matter how much even the most reasonable and level-headed players beg you, it's here to stay. I don't like that, but I accept it. You put time, effort, and microtransactions into it. So instead we fix it.
First off, we standardize the crystal cost. I don't know what formula you're using, but it's overdesigned and incomprehensible. I've even heard reports of the amount changing for the very same weapon. It needs to be some flat number, times the new level of the weapon, times the forging rank. Let's have an example, and we'll use two. I have a four-star weapon that I want to forge to level 6, and I don't want to gamble - because gambling is bad - so I use the third forge rank. 36 crystals. Easy math.
Next, the interface is bad. Sometimes it'll let me forge without the full number of crystals at reduced odds, sometimes it won't, and in either case I can't look at what the requested number is (and I can't just guess; as previously mentioned, the current math is indecipherable). There needs to be some way to view the recommended/required number of crystals at each tier, but otherwise I don't have good suggestions on how to fix it. The menu is really overblown with a lot of wasted space, but I don't really have any good suggestions for making it look better. Sorry, I dilettante in a lot of things, but graphics design isn't one of them.
Okay, best/worst for last. This is kind of an overhaul, but I think the forge needs one (that, or a drastic reduction of crystal cost). The baseline forging is 100%, but with no bonuses. You can add chances for bonuses, but that decreases the odd of a successful forging. But to balance that, you can pay in more crystals to pump the odds back up. This way, any gambling is opt-in, rather than opt-out-at-ridiculous-cost. This version would probably require higher baseline costs than they are now, but for the same price I'd rather have a guaranteed level up with no bonuses than some maybe bonuses with 1/3 odds of just losing the crystals I farmed for NOTHING.
In review: fire that guy, easily-understood costs, de-bloat the interface, remove gambling. The rest of the update was cool, but this part is terrible.
Since we're using anecdotes as evidence, I successfully forged twice at 20%. Thus, I put forward the notion that this entire suggestion is in the wrong due to the fact that it has no substance, and is simply based on op's dislike of the forging system.
Assuming you are talking about the crystal cost increasing for the same weapon as it levels up, that makes sense. It takes more and more effort to level up, a common concept in any mmorpg.
I haven't had any of the interface problems you listed.
Tl;dr Another unhappy thread about forging because the focus changed from farming ce to farming fire crystals.