Damn right it's OK! You should be so lucky someone asks you to sell out
LOL!

True. But in this case, no thanks.
Allow me to frame it this way: There are those here who learned their instrument to express their creativity. There are others who did it to garner attention from desirables. At one point or another many had to decide between one or the other, the endeavors for them being mutually exclusive. Some chose creativity, others the desirables. For many this is easy; their creativity wasn't much, or the desirables weren't much. For a select few both endeavors were attainable. I think Pino fits this select category.
My point here is that folks who rationalize Pino playing a gig that doesn't showcase his talent (and it doesn't, trust me) just because he's getting a whopper paycheck, are saying that it's good to sacrifice your creativity for a paycheck. I don't think I can speak to what "good" is, but I can think of a few ways to argue against that thought process. It basically comes to "if you're making money who cares?"
Which basically means that Gene $immon$ is a better bass player than Pino cuz he's made more money. See what I'm getting at?
So, to the OP TJH3113, I think you're right, mix notwithstanding Pino's doing a session man's gig, and that's it. It goes on his resume and when the next member of The Who croaks, he moves on to the next paycheck. Is it what we want to think of as "worthy" of a great artist? Well, he's not making songwriting royalties, so he'd better do something.
As for The Who, they like Zep were a gestalt phenomenon. The effect of the group was greater than the sum of the individual parts. Replace one of the parts and the group was no longer "magical". Stones, nah, as long as you have Mick and Keith, it doesn't matter who else is there (maybe a good gig for Pino?). But both Roger and Pete know that the group isn't the same and never will be so the idea is to reprise the old songs with session players knowing that many will pay $$ to hear septuagenarians try to look like they are in their 40s and sing songs that are 50 years old. It's an oldies act. Pino doesn't have his old voice, but then again, Roger doesn't either, now does he?
Pino's collecting a paycheck just like Pete and Roger. And like Pete and Roger, he gave up who he "was" to do that. As John Lennon said, you can always listen to the old records.