Could agree more! We also don't need to rely on reporting and waiting for bug fixes from their side (some times takes years for them to get to fix), here we do it ourselves.
I had a past with Java back in 2007, and yes if you do the heavylifting in GLSL you should be good to go, after all minecraft was a hit and originally done java too.
Mine is in C++ with OpenGL and Metal, I'll add DX in future.
Good luck with your engine it already looks very cool!