[persnickety]

The ad company wants to make ads browsing easier, therefore it created HTTP/3. I can entertain that statement.

The ad company created QUIC to make HTTP/3 possible. That's also certainly true.

What follows: the ad company created QUIC because they wanted to make ads easier.

But "QUIC exists to improve ad deliverability" is true only in the shallowest of senses, similar to "nuclear power plants exist to drop bombs on civilians" just because research on nuclear power was driven in large part by war needs. In reality, nuclear power has its own uses beyond the military.

Similarly, QUIC taken on its own merits does not have anything to do with ads. It's just another general purpose protocol.

BTW, multiple streams will not make it any faster to load ads from third parties. Head-of-line blocking only affects resources within a single TCP connection, which can only ever be to one server. That means QUIC's streams do nothing to make loading Google's third party ads easier.