"Either way, I still fail to see how this relates to the original complaint that QUIC somehow leads to ads."
"HTTP/3 uses QUIC, a transport layer network protocol which uses user space congestion control over the User Datagram Protocol (UDP). The switch to QUIC aims to fix a major problem of HTTP/2 called "head-of-line blocking": because the parallel nature of HTTP/2's multiplexing is not visible to TCP's loss recovery mechanisms, a lost or reordered packet causes all active transactions to experience a stall regardless of whether that transaction was impacted by the lost packet." (Wikipedia)
I'm a text-only browser user; I also use TCP clients with a localhost TLS forward proxy. When I visit a website I only request resources manually and only from a single domain at a time. This works great for me. But obviously it is not compatible with ads. This is because ads requires websites that cause so-called "modern" browsers to automatically request resources (ads) from multiple domains "simulataneously", i.e., "in parallel". As such, I see no ads. Not a problem, I can live without them.
However, for those who let these browsers request ads automatically, there are problems. "The web", as they experience it, gets slower. Because although the requests to multiple domains may be executed "simultaneously", and the HTTP/1.1 protocol allows for pipelining requests, these browsers cannot process the responses that arrive out of order.
HTTP/1.1 pipelining does work. Outside the browser, when requesting non-advertising resources, for example. I have used HTTP/1.1 pipelining outside the browser for over 20 years. It works beautifully for me. I am only requesting resources from a single domain and I want the responses in order. So, right there, we can see that HTTP/3 is addressing the needs of advertising companies and their partners rather than web users who are reqesting non-advertising resources like me.
As the web became infested with ads/tracking and became slower as a result, the ad companies and CDNs, e.g., Google and Akamai, sought to "make the web faster" by introducing a new HTTP protcocol for the so-called "modern" browser. (This browser, as we know, is more or less under the control of an advertising company, the same one introducing the protocol.)
Now, a web user (cf. institutional player in the online advertising industry) might conclude the easiest way to "make the web faster" is to remove what is making the web slow: ads.
But the "solution" chosen by the advertising company was to keep the ads and try to make it easier for the so-called "modern" browser to process out-of-order responses from multiple domains, e.g., ad servers, faster.
Will HTTP/3 and its use of QUIC "lead to ads". That is for the reader decide. I think it is safe to say it will not lead away from them and it could help cement the ad infestation of the web even more.
tl;dr HTTP/1.1 is optimal for sequential information retrieval from a single domain. HTTP/3 is optimal for resource, e.g., advertising, retrieval from multiple domains "simultaneously".