One of the points of my post above is that the two issues have to be dealt with in tandem rather than separately. For single winner elections - I prefer methods with ranked choices in a single election as you often advocate since it eliminates the concept of the “wasted vote” which is so detrimental to democratic values. So, if voters get used to ranking candidates, then you wouldn’t want them to be using a system like cumulative voting for the multi winner races since the ballot would look so different (even though cumulative voting is very advantageous to alternative parties getting at least some representation on councils). That leads me to something like single transferable voting which - as you say above - is an instant runoff system with a criteria to be declared a winner of 1/(# of winners + 1) and all excess votes above that criteria going to your next choice on a proportional basis.
Or to put it another way, it is very difficult to be a politician in Amerika if you have principles.