On the other hand you can lose your email address at any time if you don’t own the domain. So if Google decides they don’t like something you wrote your @gmail.com address could be gone tomorrow. And with it all your accounts you set up (as you need email usually to login or do changes).
The whole e-mail ecosystem sucks :-/
My self-hosted mail server works fine for now, but that could change at any moment.
But the NAS is in your house… which basically means if it gets flooded/burns down all your data is gone too.
I already have my data on my PC, a second backup inside the same house isn’t worth that much. But instead of relying on a cloud service I just rent a virtual server (for various things) and use Seafile to keep my data in sync.
PC breaks? House burns down? My data is on my own server in a datacenter. My server gets cancelled? My data is on my PCs.
So even with your NAS you are 100% reliant on a cloud backup still, so why did you get the NAS when you already have a copy of your data on your devices?