is it in trouble currently? No.
Will it be in trouble in the future if it carries on as it is? Maybe?

I think the main issues with the game are pretty simple and have been discussed but ill list my 3.
1. Theirs not a lot of fun content once you finished endgame and done raids (which raids don't even have scaling content you either do really easy or content that's pretty hard), a lot of the content is too spread out for the core playerbase we all have to wait a long time to get new raids, dungeons, general content, I think this issue is also more of a issue because of point 2
2. The Job Gameplay is very boring and samey, once you played one job in a category you've pretty much played all of them, tanks and healers are a prime example of this, If jobs felt different then getting clears or leveling, or doing dailys would feel more fun to do, but currently theirs very little differences which makes me question why we're getting more jobs.
3. Synching down feels awful, most content 70 and under I can't stand personally, the lower the worse it gets, this makes half of the old content just really unfun and a lot of the times you will end up having to do old content over and over if you want to level a job or just if you get unlucky.

The three things I listed generally doesn't effect everyone and I do actually like the game otherwise i wouldn't comment about things i want to see better, I don't think we will have a sharp decline but endwalker launch is most likely the "peak" of ff14 player numbers, personally I hope the game becomes more fun I've certainly been drained from playing tank a role I used to love in SHB.