Idk if my situation is relevant to yours as (I assume) you have been twinking before legion, but here goes.
In short, my answer is yes it's worth coming back. I have been playing on and off since panda expansion, resubbing once a year or so. But it never lasted longer than a couple of months. Same would've happened with legion but I discovered twinking and have now been playing it consistently for more than half a year with no doubts/prospects of becoming bored of it in the nearest future.
Again, it might be different to you as you can compare twinking before legion, but from my own experience I would suggest you to go for it.
Edit: as per your other questions - not much has changed since launch, survs/discs are dominating but I wouldn't say it is to that extent where bgs become unplayable. Sure, you get some games where it simply is not fair playing vs 3-4 survs, but that's an exception rather than a rule