I agree. I use Proton and I have exactly one service which supports GPG. It’s a cherry on top but it’s not all that useful.
The big thing is to use a trustworthy service that you pay for. It’s not bulletproof but at least the incentive is there to keep your email private and away from advertisers.
Where did you get 100 from? I’m just asking if it’s a real limit or a guess at “some manageable number” under one million.
It can be worth experimenting and tuning this value. You might even find that less than 100 works better.