That's a decent argument, but there's some speculation involved here.
Why would Yoda only go 60% of his power against Sidious? That just doesn't make since. Yoda would have given it all in that fight.
When you spend however many hundred years of something, just instinctually holding back, you just cant deprogram yourself to just flip a switch and change it. I guarantee you, if yoda could fully tap into his force knowledge, and beat sidious, but that meant him delving a teeeeensy bit into quasi=darkside, he would have never done it.