If you have noticed an FPS increase by dedicating more RAM to Java/Minecraft I would say it is coincidence, to boost FPS on Minecraft alone install a Mod Called OptiFine, you will notice massive FPS Increase.

Will allocating more RAM to Minecraft make it faster?

Allocating more RAM to Minecraft can (and in many cases will) make Minecraft perform better, but there are situations in which allocating too much RAM will decrease overall system performance. Other areas of your PC require RAM, too.

Is it bad to allocate more RAM to Minecraft?

But the bigger and more beautiful your "Minecraft" world is, the more RAM it needs to run. And if not enough RAM is allocated to the game, it'll load slowly, frames will stutter, and it might even crash.