I wish there was more transparency about exactly how the rating system works. Sometimes it seems like you can just place a bunch of random items all over your island and get a 5 star rating.
Personally, I deliberately have flowers everywhere because I want literally every piece of grass covered in flowers. It annoyed me more with the trees because when I terraformed my island I made a shopping area, a housing area and a fun fair higher up with stone path underneath so I didn't want loads of trees on those areas. For the longest time Isabelle would complain about the lack of tree variety because I don't have many cedar trees.
Honestly I preferred the old way they did the whole perfect town thing.