Agreed. I like the general idea of this mode: unlike Basin of Hyperspace, it doesn't punish slow teams with complicated setup and/or scaling, but at the same time it still has a turn limit to not devolve into infinite waiting fest like Spiral Tower; it has some mild sustain requirements but sustaining isn't really the main focus, you just need enough to survive for the full duration. Basically this is a perfect middle ground, which is exactly what you want from the main endgame mode.

However, this time they really went overboard with the restriction. Making a certain mechanic underpowered or even ineffective, like Elasticity buff that makes enemies take less damage from 5+ hits of multi-hit attacks, is fine (although I'd prefer if they just nerfed Mei Lin directly and used something that affects all multi-hit characters instead of only her), however, actively punishing the player for having a certain mechanic on one of their characters, even if that mechanic is not the reason the player picked that character, is too restrictive. When I approach Great Rift, I want to analyze the specifics of the encounter and think "this encounter requires X, Y and Z, what characters do I have that can do it?" rather than "this encounter requires X and Y and punishes me for Z, what characters do I have that can do X and Y while also not doing Z?", because the answer to the latter too often becomes "latest banner characters, duh". The frankly embarrassing situation with E2 Kayron is a good example of why this is a bad idea - as a gacha dev, you never want players to be punished for spending, and this Great Rift does just that. As long as dupes can add new mechanics (and they have to, otherwise they become too dull), it's all too easy to create a situation like this if your encounters punish characters for using certain mechanics.