You can’t get 5 stacks without blowing up. The in game description says 30% but the wiki says each stack is 5% crit which would indicate that the max is 25% but then you blow up. So really the cap would be 20%. Is the wiki just flat wrong and each stack is 7.5% with 30% at 4 stacks or is it broken and its 6% per stack with the cap being 30% at 5 (but you blow up)?
You’re not wrong. The stacking talents are all scaled to a larger overcharge pool. It’s currently only possible to hit five stacks on UC. I have no idea why. Maybe there was originally a talent increasing max overcharge on Pyro. Or maybe it was just an oversight.