One issue seems to be domination by majority?
For example, let's say 55% of electorate is hard left, 45% moderate to conservative.
Under approval those 55% can vote for all 3 lets say hard left candidates, no moderate's make it in?
RCV, once someone has gotten their candidate in, their vote is exhausted. Seems to come out much better. Still might end up with 2 hard left, one moderate, but that seems fairer to me.