I've seen so many using a Pro for PS shadows but 95%+ people own the base console? It could run like trash or be broken. 

Personally I think they should play on base console for the most part and then load the game on Pro yo review the changes as a small part of the review. 

Base console and/or PC version will be best. Either will be where the majority of players will be.

Pro consoles will always be in the minority of marketshare.

Well, I need to know if I should buy Mortal Kombat II for Genesis or 32X.

Focus on OG but also mention the differences/improvements on the Pro.

They should use both. A review is there to be used as a reference for someone who may be interested in purchasing a game, so the more information given the better.

Both? If you’ve got a PS5 copy, might as well check ti see how the game runs on one versus the other. I’d imagine performance won’t be different enough to significantly change the score though.

Review the copy your audience is the most interested in and where you can thus provide the most value. In most cases, this ought to be the base version. Of course if you can review the other version as well, even better.

Shouldn't be too hard to test a game on both consoles. That said, look at the PC space. Are reviewers using the RTX 4060 for their reviews, the most used graphics card according to Steam, or are they rocking 5090s and not even care about talking about settings? Nowadays it just seems to be set in stone that all the sliders are all the way on the right, lol.

I think reviewers on PC should do minimum and recommended specs if not low end, mid range and high end or something along those lines. Youtubers do it, they make sure to test on multiple machines especially if the game has issues. 

Base as the focus with some details about Pro.
I don't think PS5 Pro is going to account for any more than 20% of the final lifetime sales of PS5 hardware, and it might be closer to 10%.