The majority of value comes from noncommercial activity with commercial interest. More songs sell after people hear it for free on the radio. More people buy a package only after the free samples.
More license seats sell, but only after 100x more seats were free.
Contribution to FOSS is not just the (SS) code, but the act of making/keeping it genuinely Free and Open.
I don't care about McDonalds or Burger King when someone's going around with free hamburgers handouts - but if I'd been eating free Burger King burgers all along, it's a pretty clear choice where I'll go to buy my business burgers on the VC's dime.
"Mere users" know very well, with less confirmation bias or sunk-cost rationale, what makes a good product. I trusted Red Hat more when they supported CentOS - these recent actions are clearly user-hostile and eschew the main value of FOSS being its network effects.
First, you are making a completely unrelated argument. "Rocky helps sell RHEL": assuming it to be true, that is not a contribution to the open source world. It does not bring new software into the world. It is only a marketing help to IBM's balance sheet, and it helps only insofar as the open source world benefits from IBM making money from RHEL.
Second, the sole direct beneficiary of this hypothesis, IBM, apparently thinks it isn't true, and from what little comments they have released appears to have come to this conclusion after quite a bit of analysis.
Third, from my position of ignorance, I think IBM is probably correct. Why? Because the free burger in your analogy isn't Alma/Rocky, it's Fedora. A user who runs Fedora on workstations or small production servers is very likely to consider RHEL when choosing an enterprise distribution for large deployments, because they are already familiar with the ecosystem but they want stronger stability guarantees than Fedora Server. But a user who is running Alma/Rocky has much less reason to move to RHEL: they gain nothing but the license hassle.
Those Rocky Linux repos are either not code (website, wiki, etc.), and a few are tools for repackaging/rebranding an existing Linux distro's source code bug-for-bug - an activity which, by definition, does not and cannot offer anything more than the original code already did.
If I'm reading that reddit comment correctly it referred to contributions to RHEL not contributions to open source, which if I'm reading it correctly was what your original comment stated.
It seems that Rocky Linux have contributed code as open source, just not directly to RHEL.
Carl George, a principal SWE at Red Hat, claimed to have found exactly one code contribution from the Rocky Linux or Alma projects back to RHEL - a two-line bugfix in a .spec post script.
(Which is only what I, an ignoramus, would expect - if the project aims for "bug-for-bug compatibility", then it doesn't really gain much value from fixing bugs, while a fork would.)
If you think his evaluation of Alma/Rocky contributions is incorrect or incomplete, I'd be interested in hearing your POV as a Rocky engineer.
Red Hat has benefited from previous contributors, but then added a ton of open source work of their own.
RH are open source contributors; Rocky Linux are mere users.