> As opposed to what?

Opposed to distributions providing targeted updates to each package.

> Dynamic linking does not solve this problem, contrary to popular belief.

On the contrary it provably works very well for distributions.

>>- Long term maintenability: your desktop becomes a random mashup of applications with increasing complexity that you have to maintain yourself.

>Again, as opposed to what?

Opposed to distributions that do the huge work of packaging, testing, backporting etc.

>>- Licensing issues: distros review licenses (and find plenty of copyright violations while doing so). A flatpak puts you or your company at risk.

>Sounds like a good way for a proprietary software to be distributed...

This is unrelated to the lack of licensing review.

>>- Impact on the ecosystem: the more users switch to opaque blobs the less testing and review is done for proper packages. The whole ecosystem become more vulnerable to supply chain attacks.

>I don't see how one follows the other.

Supply chain attacks are strongly mitigated by maintainers doing vetting and packaging, and by distribution doing release freezing.