This is a good suggestion. At some points in our lives, we all will have to decide who to stay in touch with and who we can detach from and not worry about daily or weekly updates. If too many apps and messages/notifications are difficult to deal with, then cutting it down (to whatever is manageable) does help.
OK, what's your solution? Users of all of those apps necessarily need a phone and/or email. The apps aren't necessary. You can just email or SMS for literally all of 'em. Either you stop using them or just deal with it. How many people on here regularly use 7+ different messaging apps for their friends? In my experience people usually use one for work, and maybe 2-3 tops for personal life.
I have a personal inbox (Fastmail), three Google Suites/Apps for various companies I'm involved with, a personal Gmail (for mostly spam). That does not include any chats (mostly personal, but also some work: WhatsApp for 90%, Telegram for ~7%, Signal for 3%), then there are three slack workspaces and a Matrix/Element to keep track of. And I guess there's Twitter/LinkedIn/Facebook for misc personal/work stuff (less critical, but do get messages on there).
I would pay money for an app that combines all of this (and works) like Element One or Beeper (problem is that Signal Bridge on Element has caused a ton of problems/bugs, and I heard of reports of people's Telegram account getting banned using Element One).
OP says he has friends that say they only use Messenger or only Signal etc, and everyone has their own preference. Sounds like they have the right idea! Why be the only one accommodating everybody.