Before anything, I would like to agree and state again that I do feel like this is super close to shipping. Right now it just feels like working out the kinks to avoid future retouching being needed so soon but ofc sending it live allows for muuuuch better testing so there is nothing wrong there.
I feel PotG is more impactful then just hordes. As far as I understand it, it would be a 50-60% raw stat boost off the rip. I see this being beneficial or desirable in the content I would be wanting to use Ursa for in the first place, further cementing and validating it in the short form content. Shorter world raids, kraid taps, some horde capabilities, Towers/Monument battles, World Farming and even sillier less notable things like Amity hunting, Fishing, World bosses with Anguish are all more effective by having a starting stat boost. Sure it doesnt effect PvP but this seems to be a foot note to most people as I am happy for my actual gameplay to benefit if my PvP is less effective. Especially since this is a celestial class and I have my other options as is.
Since I mentioned I am a fan of other mechanics and youd mentioned you have tested reverse redlining I will throw out some similar concepts or attached ideas I had to that since I thought of the reverse idea for Deity rework a bit back. I feel some of these may verge on oddlly complex or awkward but if PotG isnt desirable then they could be considerations.
Reverse redlining could be maybe more of a token system? To prevent early turn turtling and also avoiding the class needing to start at lower HP(like you would see in Gilga/Ward gameplay) there could be a system that every turn you are above, say 50% HP, you get a stack or token this increasing your stats like any other passive. [All just spitballed numbers but you could make whatever] But it could work as such, when the battle starts you will gain the token on the start of your turn to give a boost right away or after turn if you dont want it to accrue so fast. Each token will give maybe ~25% stats. As long as you stay above 50% HP your next turn you will get another token up to 50%. However, if you are to dip below whatever HP marker is set(50% in this example) you now lose 1 token and if your next turn comes and you are still below 50% you will lose another. I think around a 75% stat boost is fair in this and could even implement a small HP gain if youd wanted to make it feel more synergistic or provide stronger identity in this.
Reverse lining could still exist as well within the same realm as current Gilga mechanics which was my original idea, just with mana. Boost Ursa's HP again but make it start with less HP, whether thats 50-60ish% or so. Thus starting with little passive but once you max it out then you are getting a good stat passive without too much excessive work for upkeep. Since u arent actively using HP like ward you could have an HP drain or HP drain on Attack skills and then maybe disable it when the Apex meter is full. This gives a quicker access passive that is still something that requires work to make use of, aswell as making it not busted for PvP. The boost would also prob be in that 50-60% realm
Apex lining is also a suggestion that would be in line with identity but does punish Apex use a bit but depending on the gameplay could be seen less as punishing and more as a trade off/debate(when done well I think players love this, making a decision to either use a big move/buff or keep your stats up). Since Apex is meant to charge faster then having your stats scale with it allows you to charge you stat passive pretty quick still. I guess this would also make it akin to Ara in that their stats scale off Apex just in opposite manners which is sort of cute. I would only worry that Apex charge can be inconsistent depending on content so this could feel like a passive we dont get to touch too often in that short content. Happy to continue spitballing if its worth but no more room on this message :P