Nirvana doesn't seem like a very apt comparison given they only made three studio albums. There's a pretty clear arc in those three records, and from my perspective they never feel as same-y as Beach House within the same record. I like Beach House generally, but definitely relate to the sentiment of listening to an album and finding little variation, and then experiencing the same from album to album. I did think 7 felt like a change of pace, but didn't much care for it.
Nirvana is interesting. Bleach was heavy and pretty unrefined, and only in hindsight did you see the genesis of songsmith Kurt (for example, About a Girl) that emerged on Nevermind. Then In Utero sort of fused the noisier and unrefined side of Bleach with the songcraft and more polished writing of Nevermind. I think that's probably why many feel In Utero is the best summation of what Nirvana was over their career, and fits within an arc that makes pretty clear sense. It is interesting to think about what might have happened after that record had Kurt not killed himself. I do think that if they were five or six records on mining the same sound as those first three records people would have probably started to criticize more. Even Kurt after In Utero acknowledged he wasn't sure how much further they could take their sound with the same lineup and setup, so it's interesting to wonder what might have happened.