[kortex]

Not a network engineer, but I expect TCP and UDP traffic are currently shaped differently by ISPs, possibly with preference to TCP. If your connection is solid, there isn't a huge benefit to QUIC, so you may end up seeing a slight degradation.

Syncthing uses a bunch of protocols by default to find clients, including TCP, QUIC and a few others. If you want to have some insight into how your network behaves with these protocols head-to-head, spin up syncthing and wireshark.

[vbezhenar]

That's definitely not the case with my ISP. I'm routinely using IPsec VPN which uses UDP packets and the only (barely) noticeable difference is +100ms latency. Actually I'm often getting better Internet experience with VPN, presumably because of different routes to VPN server and target website.