Season 5 was also hated when it was airing even though everyone loves it nowadays. I still think it's one of the worst seasons, oops.
S7 did have some pretty terrible themes that the decision to make themed semi-finals wasn't even the worst of it. re: the second Beatles week, iirc, they were originally set to do "Current iTunes Top 200" or whatever but were having issues clearing songs/licensing them for iTunes, so they changed it to a Beatles week redux at the last minute. That inadvertently meant S7's themes went 80s (T16)/Beatles (T12)/Beatles (T11)/80s (T10, with Archie being the exception in 1990).