I'd much rather have the extra speed than being able to store a couple of extra games when I'm still going to need external storage regardless. Xbox Series X's ssd will be better than a standard SSD thrown in a PC with no extra attention given to it and PS5's SSD will be better than the one in the xbox. When you are talking a few games difference let's say 15 games on one console vs 18/19 on the other that's really not a significant difference, nobody really plays that many games in the same time frame anyway. I have over 46 on my SSD and I probably play no more than 5 of them within a months time, many of them haven't been played in over a year.
I know some people wrongly think the PS5 SSD size (as opposed to 1TB) was chosen to be cheaper but they've explained that it came out that way due to the customizations they've done and basically if they wanted to increase the size of the included drive they'd have to double the size of the SSD to be 1.6TB which would end up being too expensive. Yeah we can put our own NVME SSD in after Sony confirms each one but those are still going to be so expensive I think people will more than likely just use cheaper external drives for storage only and moves games around.
You know the Xbox SSD is custom designed not just one you slap in a PC jeez.