By overpowered I mean value to cost ratio is strong. Even giving it 2 frigates + 1 caravel would be good
The value to cost ratio was already very strong at 2700 3 caravels. A 900 gold discount is pretty huge. The problem was the cost of saving up to 2.7k, and the gold sink like you say. Making it more valuable won't solve this. It will either make the wonder a must have to easily lock top, aka overpowered, or it will still cost too much to get.
Changing it to fireships is a bad idea, fireships are in a unique place where they come in and out of the meta.
Pent mass is the only strategy employed at top right now, and as such fireships are very useful. I would say they are firmly in the meta right now. I don't think they are leaving anytime soon as long as mass is a thing.
The change may not be as significant as you think.
2000 gold is far more easy to build than 2.7k. Iron works is a doable investment at 2400. Sometimes I have 2 caravels in top anyway. I would rather just build this wonder and save some gold. The cost reduction also makes it less of a 'gold sink'. The caravels will fall off later, but honestly the 400g saved in the stages where you would be getting caravels outweighs the cost in the lategame when the game is usually already decided.