>I should never have allowed even one flatpak

I don't think that's the best conclusion: these days, disk is cheaper than it has ever been, and that "foundational" 8 GB will serve all the Flatpaks you want. Installing apps from packages sprays the same dependency shit all over your system; Flatpak was nice enough to contain it, so you immediately noticed it.

Flatpak is a good idea.

It's at best a mixed bag which makes it harder to fine-tune apps on your system and with limited security benefits (which again become harder to improve yourself).

https://madaidans-insecurities.github.io/linux.html#flatpak