But its extremely common in big projects to have atleast 20 prs open with long build.
kubernetes has like 1100 open prs atm ( each pr with 5 25 min builds). What should a project like k8s do for CI ? would require insane computing power to launch 5000 builds for every merge.
Getting from here to there probably requires a transition phase. In the long run though, if the time spared/lost waiting for PRs, developers context switching, resolving conflicts and dealing with errors (that will appear anyway) is invested into improving the quality and speed of automated tests, you end up in a much better place.
I'm not saying it's an easy thing, but in my opinion this is what development teams should strive for.