Updating the source code of your software goes agains the spirit of a decentralized network? How? The whole point of decentralized networks is that people with different source code/implementations can communicate with each other.
That's true, compiling rust is harsh, but we're are talking about server admins and sysadmins here, I have faith that sysadmins will know how to compile and deploy rust.
TIL the Lemmy Server code is written in rust, hell yeah
Yes. That's what the word "operator" means. You need to operate the software that the network depends on, or trust someone who does. You see this a lot of time in the Bitcoin/cryptocurrency community as well, where node operators complain about the changes "forced onto them" by developers. Ultimately, it's a labor problem—if someone else is writing your code for you, and you don't know how to modify it, you're at the mercy of their decisions.
There are services like that for Mastodon [0]. But a provider that lets you host from a choice of e.g. mastodon, pleroma, lemmy etc would be interesting.
masto.host has a great deal of restrictive, somewhat arbitrary content moderation policies for what is basically just a server host[0].
Since that the original problem is that admins may want to override built-in censorship policies to suit their instance's needs and values, I don't think an even more censorious centralized authority is a great example of a solution.
Masto.host is run by one of those people who put inflexible ideology ahead of the wants and needs of their users. That is ever a concern when having a third party set up and manage everything for you.