Not submitting but I have a few qualms about the focus of balance in this metagame (seeing as it will feature in the upcoming PMGS):
Celestial Curse:
The fact that this move, of all things, seems to be the "super broken" one doesn't reflect well on the balance focus. For starters, a vast majority of these Z-Moves on actually good attackers will be OHKOes or near OHKOes, so the whole 1-HP into weather/passive damage (lol how reliable and efficient for a 1 time use move) isn't a particular standout ability. This move isn't safe at all as long as a Dark-type is present on the opponent's team and Gothitelle isn't exactly the most offensively threatening Pokemon outside of this move nor is it easy to get into play. Also, you're both giving up your team slot and your Z-slot for non-Shadow Tag Gothitelle. A Pokemon that's like C tier viable in ZU.
TLDR Don't ban the Pokemon that gets a 1 for 1 trade in the best of situations
(lol)
"Overpowered" Z-Moves on unquestionably shitty pokemon
Why are all of the "broken" moves on the sheet looking at the move in a vacuum and not considering the fact that, well, you're using a MEOWTH in OU (not to mention fucking Greninja has virtually the same move but that is somehow ok) or any of these others unquestionably bad Pokemon. Swellow having a 200 BP attack with a self burn is just basic guts Swellow with a one-time more powerful Facade. No clue how that is too good for OU. Stantler needs all the help it can get, it's still a stantler so setting up won't be as easy as its made out to seem even with a 240 BP attack. The Delibird boost is questionable and likely hard to code anyhow so that's fine to go. Meowth is Meowth. You have like 50 base attack and a 40x5 BP move is supposed to be overbearing how? The Speed boosts? What's a Meowth gonna do with that Speed? Alolan Persian's move lowers accuracy which is annoying but it's also blowing your Z-Slot (and teamslot) on a stat-dropping pivot move. If anything I'd make it also full heal the incoming teammate because as it stands it sounds weak and low impact, like a no-death memento (not that Persian will be putting in work regardless of being alive or not). Guzzlord being the questionable UB ability is lol when Kartana is sitting there with a Steel-Z that also gives it free reign to massacre the team with boosted Leaf Blades. Guzzlord needs the help.
Why would you buff these already A+/S tier OU threats oh god why
This is a case of only-ok Z-Moves (comparatively) being given to already amazing Pokemon. Greninja effectively gets a more nuclear Waterium Z (especially in Ash Form, at 300 BP), Magearna gets a Z-Fleur that also clears the field, making it an even better Hyper Offense pick than it already was, and Kartana snowballs like there's no tomorrow.
So overall my thought process on balance is as follows:
Z-Moves on basically anything below UU need to be really fucking good in order to make a pokemon busted. A really good Z-move is still only one time use and still means that you're burning a teamslot on something stupid like Gothitelle in an OU match. Don't give S tier mons better Z-moves. This should be self-explanatory.
Thanks for listening to my TED talk