For now. The same thing that happened to GoodReads will also happen to Letterboxd. Nobody wants to pay for a service like that to stay true to form in the long term.
There's already plenty of group think with certain films. More and more very recently released, popular films are shooting up to the highest rated within a few days. Letterboxd should probably account for the recency bias a bit better.
Right, which is why I think there's more value in finding a couple of individuals whose tastes resonate with your own, and watch their favourite things, rather than pay attention to aggregated scores.
I only casually use it to find books I might like. So far I've not noticed anything changed since Amazon acquired it (didn't even realise they did, in fact)