I know day one opinions can be fickle, but I feel like this update will irrevocably change the trajectory of the game in such a way that needs to be addressed.
To get to the point, Guest Stars should not have stats. At the very least, not in their current state. Locking such a significant stat boost behind 4 million canopy and universal retakes (which are already scarce) makes them fairly inaccessible and exacerbates the stat grind, especially given the context of an economy that is not at all tuned for the feature (and judging by the pittance that is the Show Me Your Moves pf, I doubt this new one will do much). The evolving mechanic is also poorly thought out: when optimizing move stats, you can pretty quickly gauge whether or not to keep upgrading a move. Having stardust increments tremendously obfuscates this, forcing you to spend a rare resource to roll instead of just coins. If it rolls poorly, you're just out of luck.
A lot of people are doomposting about GS' implication on Rift, particularly on defense. At this point, it's too early to make any absolute judgment on their disruption to the meta; I will say on my part, I don't it will affect things too disastrously because you can feasibly shift around just three GS if you're concerned about stats (obviously more if you want to specialize, but it still heavily favors offense).
I wouldn't count this as a silver lining, though. The crux of the issue with GS stats is they're simply not compelling gameplay-wise. If they won't ruin Rifts, one certainty is that they will be a pain to upgrade and optimize. GS were intended to add a layer of nuance to gameplay (and this I appreciate), but implicating stats shifts their focus so heavily onto the stats min-maxing that it overshadows everything else. Late game SGM basically converges to one big stat check. And even if having all maxed GS isn't the intention, or is supposed to be a luxury rather than an expectation, that doesn't matter. In practice, the core substance of GS - the relics, the prize fight, the stardust, the retakes - is upgrading them. GS as a whole don't feel good. I don't want to worry about more upgrading in favor of the same system, and I don't want another prize fight to clutter it up. I want a new system.
To put it politely, though, I don't think a lot of the idealist criticism in this thread is any closer to an improvement. I feel like a lot of the hitherto disdain toward this update is more a means to legitimize latent cynicism than analyze the problem in a meaningful way.
Story mode is often echoed as a panacea to the game's stagnation. I think it would be nice to have more story content, but it's disingenuous to say a lack of new story content is why people feel burnt out. Ultimately, story mode is still a one-time occurrence that doesn't expand on gameplay. If people complain about the repetitiveness of Parallel Realms, why would adding master origin stories be any different? I see a similar trend with a perceived lack of fighter reworks. There are a few variants I agree could be retouched, but 1) we've had quite a few recent reworks and complaints of game stagnation have not slowed and 2) hasty reworking can very easily lead to the homogenization of variant abilities for the sake of meeting the bar of the current meta. These are band-aids on a much bigger problem.
That problem is, as alluded to, a lack of gameplay variety. As in, the core structure of this game has not changed. Between all the different modes, the approach and end goal is always the same: look at opponent team and match modifiers, build an appropriate counter, and defeat the opponent by counteracting the abilities and modifiers. You can say dailies and Rifts serve different purposes, but at the end of the day, between each independent battle, it's all the same. And with great predictability. Modifiers are set in stone with virtually no real variety. Parallel Realms might as well be another prize fight.
This is what makes some variants "obsolete". When the goal of everything in the game is the same, there will be variants best at that one goal and variants that will never find a place. The game needs something to reward abilities and approaches that aren't just Deadeye and Precision through a stock defense ability. Something that makes use of an entire collection, or is randomized to keep me on my feet. Or at the very least, something that doesn't amount to a series of functionally identical battles.
This update as a whole feels like a half-baked idea stitched on an increasingly bloated infrastructure. Upgrading GS means another prize fight to worry about. Buying stardust means another currency piled onto Rift. Coming from someone who likes Rift, I don't think the game mode was meant to sustain all of these crucial aspects of the game. I don't think prize fights were meant to be the principal source of new fighters, income, retakes, shards, the monthly "event", and now GS, all simultaneously. These resources should either be spread among new game modes, (adjusted for time commitment of course) or there should be a way to obtain the same resources pool through different means.
A manifestation of this "stitched on" feeling (and perhaps a less "serious" criticism) is the UI. Maybe I need to get used to it, but the collection UI feels clunky and discordant. The icons are nondescript and incohesive, the moves bar is cluttered, and GS now complicate move loadouts. And most egregious to me, (and objectively the least consequential detail) the GS relic render looks really bad. There's no lighting or texture, the star looks amateurly put together, and it all presents more like a CAD model than anything else.
The mistakes of this update have already been made. I don't think at this point GS stats can be rolled back. I'm also still not cynical enough to take the "dev's don't care about the players" angle, but this definitely isn't helping. Ultimately I hope none of this turns out as bad as a lot of us think it will, I hope we will see more transparency in the future, and I hope everyone seriously examines the state of the game.