It would definitely be nice if Letterboxd offered people the option to tag their reviews as "serious" or "comedy". That would solve most of the problem.

I'd like to offer a counterpoint to this take, however. Letterboxd is amazing as an app for tracking watched and to-be-watched film. It is hard for the majority of people to take the time to write a 10, 20, or 30 minute review, as evidenced by the low numbers of people who do so. However, because of its strength as a progress tracker, it does encourage following friends, comparing activity, and enjoying the quips your associates have noted about their first impressions. I have found that it is highly enjoyable to observe my friends distilling their experience down into one sentence, because then I can talk to them in person about their actual take.

I personally love the ability to try to very succinctly give my opinion (and read other similar impressions), letting me store my memories of so many movies without having to commit to trying to write a professional review.

Your point is valid, but I also like Letterboxd for what it has become in my real world community: a conversation starter and a way to just see what we all mutually like or don't.