Unless you have some kind of special circumstance you can leverage it's hard to beat TCP. You would not be the first to try.
The fundamental congestion control issue is that after you drop to half, the window is increased by /one packet/, which for all sorts of artificial reasons is about 1500 bytes. Which means the performance gets worse and worse the greater the bandwidth-delay product (which have increased by tens of orders of magnitude). Not to mention head-of-line blocking etc.
The reason for QUIC's silent success was the brilliant move of sidestepping the political quagmire around TCP congestion control, so they could solve the problems in peace
QUIC is real and works great, and they sidestepped all of that and just built it and tuned it and has basically won. As for QUIC "sending more parts of the page in parallel" yes thats what I referred to re head of line blocking in TCP.
Unlike TLS over TCP, QUIC is still not able to be offloaded to NICs. And most stacks are in userspace. So it is horrifically expensive in terms of watts/byte or cycles/byte sent for a CDN workload (something like 8x as a expensive the last time I looked), and its primarily used and advocated for by people who have metrics for latency, but not server side costs.
That's not quite true. You can offload QUIC connection steering just fine, as long as your NICs can do hardware encryption. It's actually _easier_ because you can never get a QUIC datagram split across multiple physical packets (barring the IP-level fragmentation).
The only real difference from TCP is the encryption for ACKs.
Some NICs, like Broadcom's newer ones, support crypto offloads, but this is not enough to be competitive with TCP / TLS. Especially since support for those offloads are not in any mainline kernel in Linux or BSD.