I doubt the bulk of battery life is lost in visual effects, especially if turning them off apparently does not help.
I’ve subjectively had battery life regressions for most iOS updates until the first minor version update or so, but that might also just have correlated with extensive re-indexing of Photos and things like that.
You cannot turn them off unfortunately, reducing transparency through accessibility only tweaks some constants in their physical simulations, it doesn’t change the rendering complexity.
