Web and email are two different things OP. Yes, they both suffer from centralization, but email is more difficult to decentralize.
Anyone can set up a website and anyone can view it. Chances are it will be indexed by Google. So there's nothing stopping people from setting up their own websites and other people using it. The reason people don't do it is probably because it's not worth the effort for most people. Hopefully, Fediverse services take off and become and outlet for people that don't need a website.
Email is a different story. As you've found out, the major email providers will flag emails from small servers as spam. Which forces people to sign up to the major providers for an email address because their small email provider "doesn't work." So you can't just set up an email server and send and receive emails to everyone.
Spam may be a legitimate problem, but the major providers blanket ban too many email servers to believe it. It's probably to:
1. Stop competitors from taking market share.
2. Stop competitors that don't share emails with the NSA.
I think email is a dead end for decentralization. It was made in the 1970s for small networks where people trusted each other. There's no inbuilt solution to stopping spam or address spoofing. If these issues are solved (as well as being practical), then there is no legitimate argument against stopping connections with small servers.
I like Bitmessage, although it hasn't been updated in a while. It uses proof of work to stop spam and addresses are based on cryptographic keys.http://bitmsgdyvsmwgsimkxplisxbzpewvkhfm3fmomzd63apaymaxiznz6ad.onion/Main_Pagehttps://bitmessage.org/wiki/Main_Page