How to fix uneven subfloor

I’m redoing my bathroom and the original floor joists are uneven. It’s a 5x8’ space and there’s as much as a 3/4” difference in the slope. I’m currently stacking shims to make the plywood level, but wondering if it’s not okay to stack shims for that much of a heigh difference? Should I cut down strips of 2x4 instead? Or just lay the plywood and use self leveling compound? I am going to be laying cement board and tile on top of the plywood.