Prone isn't as strong as it was in 4e, but it can still be a solid tactical choice. You just have to weigh if it's something your party can take advantage of.
The biggest and best advantages of proning are as follows:
- reduction in movement speed (halved)
- Advantage on close (5' range) attacks (includes ranged, so it negates the disadv imposed there)
- Impose disadvantage on the target's attacks
Is prone worth burning your whole action on? Probably not. Is prone worth it if you can add it onto an attack you're already making? Possibly.
This is really a question of party composition. If your party favors ranged attackers (as yours seems to), prone is a bad play pretty consistently. You'll inflict disadvantage on your buddies and that means they'll miss, a lot. However, if you've got a melee rogue or other melee combatants in your party, they'll probably kiss you if you can prone someone consistently. The rogue gets a huge damage bonus with advantage (like several DPR) even if they can already get their sneak attack off, and other melee combatants also get a big boost.
Advantage on their attack rolls plus disadvantage on attacks against them is great. Granted, it's easy to get out of this condition, but if you can do it right after your opponent's turn then you'll get a full round of benefits.
(I think it's worth mentioning here that Advantage/Disadvantage are much stronger benefits than CA was in 4e. Which means that the relatively limited movement restrictions don't matter quite as much)