You might have a point about Tumblr... I've definitely thought about it, but you could say something similar about any platform, including social media and Google.
Even at the server level, or the power company, or DNS, or any external service, etc, etc, etc.
Even with Static Sites, they have to be hosted on Object Storage, which can still be zapped by big tech interests who manage the object storage.
There might be some decentralized encrypted object storage on blockchain technology, but it's still young.
Last time I looked at it, a promising service had gone under. (LoL)
Point being, I think we just have to keep things in generic niches, when possible.
I'm doing a lot of things in Tumblr, now, though... even controversial niches, but there are others out-there, as well, and I think we're still a bit protected by discrimination laws, perhaps.
I do think about what you're describing, but I also don't know how to completely avoid it.
Even if you build a list, you could argue that mail providers might start blocking your stuff. (haha)
Collect home address or phone number? Then mail companies and telecom start blocking you...

There's a certain level of risk, in terms of dependencies, and I dunno how to completely escape that, man.
But yeah, I used Bootstrap Studio's WYSIWYG to build me an easy, simple, fast, generic HTML template, and I used that thing to build a variety of simple sites.
I also had my Tumblr theme built on the exact same template.
Honestly, though, HTML sites are so cheap and performant, I think it pays to just find a guy on a marketplace to make them cheap for you.
You just drag them into your object storage on Azure with CyberDuck, and deploy with Cloudflare.
There are some good tutorials on YouTube for that kind of thing...
When you break it all down... HTML is the foundation of web... it's the cleanest, simplest, most performant website possible. (pretty much)
If I could go back and advise myself, I'd just tell myself to hire guys to build simple sites, and for extra features just use external saas or free tools, or something...
But really... it's just all about simple sites you don't have to jack with, or spend hours trying to find some fix for... I literally wasted thousands of hours on Wordpress sites, in the past...
You can make Wordpress sites static with things like Hardypress, but dynamic plugins suffer.
Anyways, yeah.. it's all about the simple.
Gotta get sites deployed and stable! (so many better things to do.. lol)