Yeah I'm cautiously optimistic that maybe they'll be bringing some of that end to end encryption tech with them and making Notion's very powerful system more privacy respecting.
Maybe they also acquired them to help fill in some of the gaps like the calendar you mentioned.
At this point... I'm rooting for Proton. I currently have Proton, Privacy, Bitwarden, and Standard Notes. Proton already has an "almost there" replacement for Bitwarden that's got (IMO) a better UI and better integrates with SimpleLogin. They've talked about expanding SimpleLogin to phone numbers and credit cards which would gobble up Privacy for me. They have a fundamental notes system in Pass (their password manager). If they fleshed that out to where it could compete with Standard Notes (... which while getting better has always been a little clunky) I could see myself consolidating around their ecosystem.
At the same time I might stick with Bitwarden and Standard Notes just because I think Proton being a "monopoly" of sorts isn't necessarily for the best.