I'm on the fence concerning collections - while I feel like I'm constantly 'missing' the latest and coolest, for the amount of time I actually put in this game. I'm very casual, I typically only put a few hours per week, usually no more than an hour per session, so I barely do more than the story-driven campaigns/LS episodes.
Most of the time I'm just running around in seasonal stuff or hopping the world boss train here and there. Last summer I had a little more time, I actually set my goal on getting the skyscale mount and it nearly drove me nuts (caveat: I tried to gather mats as much as possible rather than opting for gold farming to buy them instead). That's right, anything beyond the basics, ie the optional/advanced content, that I normally don't delve into by lack of time to put into it (it's optional anyway, right?) feels like an actual accomplishment - yes, 3 years after it was added to the game, who cares.
Just be to be clear, I'm not complaining - this optional content was there for me when I was ready for more, I only completed one thing out of dozens out there, and I'm totally fine with never getting to the end of the game.
I started working towards a gen 2 legendary weapon, I'm on the 2nd precursor and looking at the gifts I will need to make, I'm positively certain I won't be done with this for at least a year. I'm serious. And I'm fine with it.