I wasn't at Sectionals, but based on TN state tourney, no D1 level players were playing at 4.0. The TN guys fresh out of college or under 21 would be good non-national ranked division 2 players, some of those guys at 4.0 went on to southern, some were on teams that didn't win TN (am I an expert, no, but I've played at that collegiate level way back when and tennis playing and watching is a big part of my life, always has been). The strokes of some were near D1, but not the level of consistency nor the tactics. Competitive 4.5s yes, easy, and no, not 50 year old guys with crafty doubles skills, legit singles tourney contenders in the heat.
Still might have to bow down to TX for sandbagging, got a friend (yes, he shouldn't have sandbagged, but he is still a nice guy, just too obsessed with nationals) who self-rated at 3.5 and went to nationals doubles and singles non-team few years ago, had a super-champ pedigree in his teens, was not yet 30, and in 2 seasons was bumped to 4.5 where he now wins often at singles and doubles. Stuff like that is still maybe slightly superior to Southern action this year.
Personally, I'm not even sure I would have the mental whatever it takes to self rate at 3.5 and just go out destroying everything opponent, it would feel strange, awkward maybe. But perhaps sectionals 3.5 self rate vs. self rate is competitive lol.