

Very good ideas, but I don’t agree at all with your estimations.
For example it is terribly difficult to self host email, and very few people actually do it. Contrary to your estimation. It’s not because of the server software, but because of the fight against spam etc. that costs so much.
You are focusing on only one “top” and so you can’t see the reality. You are scoring centralization. Not decentralization.
Better if you look at the share of hosters at the “lower end”, the ones that actually do self hosting, like:
% of servers with up to 10 users (counting only natural persons).
% of users on servers with up to 10 users (counting only natural persons).
Proxmox is (nearly) a class of it’s own. Yes, you need it.
You are not limited to lxc. Just run one or more of these Debians in VM’s inside, and they can docker then as needed.
Don’t forget to use the templates in Proxmox.