Can people whine that they spent the last couple of decades investing an expected amount of planning only to have Disney reinvent the wheel, effectively pulling the rug out from under them?
The big advantage FP+ offers is getting FastPass for late in the day without getting to the park early, which I have no problem admitting can be handy, especially on arrival days. People who tend to be pro-FP+ criticize legacy FP because it favored early risers; Fastpasses were gone for headliners before they arrived. I understand that would be frustrating. However, when people make the complaint that Fastpasses weren't available at the 60-day mark, those same FP+ champions remind them they can always ride stand-by. Why weren't they such vocal proponents of stand-by lines when they were the ones unable to obtain a FastPass? That was still an option when they couldn't get a paper FP. Furthermore, under FP+ the new go-to argument is "if you don't like advance planning, don't go to Disney," but couldn't someone, under legacy FP, say "if you don't like waking up early, don't go to Disney?"
This is the exception I take with the militant FP+ crowd: the inconsistency of their arguments. Every argument they make to champion FP+ can be reverse-engineered to support legacy. It's just a different side of the same coin.