I used them for some things, but other things still don't work quite right. Take Steam for example. I do love flatpaks for testing out apps, things with really finicky dependencies, or pinning a specific version of a software that I want to continue to work in the future. However, for most things, Arch + AUR just covers all my needs without any hiccups.
To me flatpaks are sort of like NixOS. All the benefits they provide aren't something I need on a daily basis. Rolling back works just fine 99% of the time with downgrade. I already have system backups. Despite what some articles might insist, things don't just break all the time. I'm not running untrusted software.
Basically no solution is perfect, but they don't need to be. If the benefits I gain can be recreated through other methods without the tradeoffs they introduce, then I will go with that. Of course, that isn't to say they don't have their place, but sometimes I feel like some people think that "being designed from the ground up" to handle certain use cases is always better than whatever "cobbled together" thing we currently have and that isn't always the case. I'm specifically quoting those two phrases because these are the exact phrases you will hear projects using to justify their existence. In fact, I would go so far as to say that some people have outright confused modularity for "cobbled together".
One last example I want to make is that I make use of projects like the fish shell and helix editor. In these cases, I find the features they introduce to be worth the tradeoffs and work better because of being designed "from the ground up" to do what they do. However, I don't make use of immutable systems, containers such as docker, or say filesystems such as btrfs. The features they provide are not useful enough to me compared to the problems they introduce.