Are paratroopers worth it?

Probably not, they are only useful in very few cases. Still, you should try them and see every once in a while so you can learn.

If you want to do something that recuires the skill and expertise of paratroopers then yes build them but other than that don't bother, like Carking mentioned,it only serves a certain purpose for a certain situation

I would build a few to break any stalemate you encounter and it is good to practice with them so you their capabilities

You probably shouldn’t even research them until they are needed, which is literally never. It’s just a waste of resources if you do research them and not use them