I think maybe it's easier for an adversarial network admin to block QUIC altogether.

The hope with QUIC is encrypted tunnels that look and smell like standard web traffic are probably first in the list of any allowed traffic tunneling methods. It works (surprisingly) a lot more often than hoping an adversarial network/security admin doesn't block known VPN protocols (even when they are put on 443). It also doesn't hurt that "normal" users (unknowingly) try to generate this traffic, so opening a QUIC connection on 443 and getting a failure makes you look like "every other user with a browser" instead of "an interesting note in the log".

I.e. the advantage here is any% + QUIC%, where QUIC% is the additional chances of getting through by looking and smelling like actual web traffic, not a promise of 100%.

Blocking QUIC blocks a sizeable fraction of the web