So I was thinking, if we just use the raw maths, ignoring relativity for a second:

1) Photon Torpedo = 45.88 Megatons to 62 Megatons

2) Quantum Torpedo = 112-257 Megatons

So that's 188,279,999 Gigajoules for a low yield photo up to 1,075,287,999 Gigajoules for a high yield quantum torpedo

Now these torpedoes are ~250kg in weight, so not super big.

So if we take Warp 9.975 to mean 2,739C (Voy: Hope and Fear) that's 821,131,542,462m/a

So that means a 250kg object at Warp 9.975 would impact with 84,282,126,253,253,000 Gigajoules

So in combat situations like the Dominion War, why did we never see FTL kinetic weapons?

I mean, in this example the kinetic torpedo is 7,838,097,817% more powerful than a high yield quantum torpedo.

Even if the Federation didn't do it, why aren't others? Plenty of others out there that would have minimal qualms about unleashing something like this on a planet for example, strap a warp drive into a box and load it up with weight, about as simple as you can get on a weapon.