Re: "getting patches reviewed and accepted into upstream is painfully slow"
I understand what the OP was referring to, but it's fundamentally incoherent to suggest that we should be "punished" for the RHEL source change by...upstreams refusing to merge changes we are intentionally sending upstream to make them open for everyone to use. It just doesn't make any sense.
You might think it's a common sense requirement, but holy cow, no. The idea that RHEL needed some secret sauce was deeply held at RH for years. One reason Fedora and RHEL have completely different testing processes is that for years it was policy *not* to upstream any RHEL tests to Fedora because it'd be reducing customers' 'incentive' to pay for RHEL. There absolutely were cases where changes were intentionally kept downstream and *not* upstreamed because of the idea this provided some kinda justification for RHEL sales.
Of course, this wasn't the idea of any *engineers*. As you say, nobody wants to actually have the work of maintaining a giant patch set. (Well, waaaaay back in the early 2000s it was kinda more common and could be a kinda badge of pride for distro maintainers, but that mindset went out ages ago). But it wasn't the engineers setting the strategy, of course. If engineers set the strategy the RHEL source change wouldn't have happened (but also, the company would probably have gone broke decades ago, because engineers are terrible at making money.)
Convincing folks that this was wrong and the best thing for everybody is to upstream changes was not a minor effort (which is why it has a catchy name - "upstream first" - and internally it's a whole darn project with documentation and training courses and the whole nine frickin' yards). We're pretty good at it now, but it was absolutely a process to get everybody to buy in. (Not taking the credit for that myself, it wasn't my project.)