To be fair: snaps can work for all kinds of things all over the stack from the kernel to individual applications, while flatpak just does applications. Canonical is building a lot around those abilities to handle lower level things, so I guess it makes sense for them.
IMHO flatpak does the applications better and more reliably and those are what I personally care for, so I personally stay away from snaps.
Canonical could have done a lot better with the explanation message here. The idea is to push apps towards XDG compliance and the use of things like Portals.
That said, unlike Wayland, portals really aren't there yet from a UX perspective, especially for an app that is heavy on file transfers.I prefer what Flathub does where it puts a nice green checker beside your app for XDG compliance - it's an encouragement, but not an enforcement.
This post title is misleading. The developer was working with Snap until Canonical didn't allowed it anymore. He's pissed with the policy enforcement which is strictly speaking commercial and as bad as Apple's afaik...
Canonical has been taking bad decisions for quite some time now, and this developer was trying to reach Ubuntu users even while probably knowing these. Which makes sense, of course. The point being that this dev's disappointment seems quite specific in these notes (against Snap), and imho he might work again towards shipping their app through Snap if he was allowed to. My comment compares Canonical to Apple, to give some context of where Canonical is at so many other idiosyncrasies (for example, I also heard other bad stuff about their H.R., in particular a way too lengthy hiring process.)