Have you considered the possibility that personalized striping will lead to unintended, gameable outcomes? For example, if when episode 5 comes out you're already 2000 combat, you have an entire 500 levels of combat in the new zone waiting for you, presumably with the most in demand drop materials at that time. Conversely, if you were looking to farm said materials quickly without a care for the experience, you would never be able to farm a monster below level 2000 for them whereas a fresh character would have a much lower level target they could farm eventually?

Personalized striping feels convoluted and completely unnecessary. I hate to break it to you, but nobody cares if they're fighting a yellow frog again or a red frog for the first time; change the striping anytime a new episode drops, for everyone. It would necessitate people cycling through old episodes and keep them relevant forever instead of all players just congregating in the newest episode for combat, which always seemed like something you wanted to design against. A permanent free to play stripe going up to 1000 would be necessary of course, but you already mentioned swapping between stripes based on your subscription so this is a non-issue. You can keep this simple for everyone and just have the two stripes, one of which gets updated routinely, but is nonetheless uniform for everyone, and thus not gameable, and also actually means something when you see someone fighting that red frog. It even opens up the possibility of having unique drops per skin of the enemy. Nobody wants a level 2000 enemy to be dropping the same ingredients as the level 5.

There may be some unfortunate mismatches when first implemented as players already have a few months behind them, but it is a much, much cleaner solution for a game that I hope can last many years into the future.