This is an interesting topic. Some thoughts of mine:
First, your striking scenario is "any tough guy who never trained striking" but your grappling scenario is someone who is "talented." Is there no such thing as someone "talented" at striking even if they have "never trained in striking"? Second, grappling is not more innate than striking. Literally anyone can throw a punch, but not everyone can even lock up an effective choke, to say nothing of arm locks and leg locks.
It might also be useful to consider how MMA fighters like Gary Goodridge and Rampage went into K-1 and upset top guys like Mike Bernardo and Cyril Abidi, but K-1 fighters like Cro Cop and Peter Aerts didn't come to MMA and upset Nogueira or Shungo Oyama with submissions...they got submitted.
A noob can wing punches. I've never seen a noob wing an omoplata.
We can add to this Jeremy Horn getting tapped by Ebenezer Fontes Braga, Masakatsu Funaki getting caught by Jason Delucia, and Manabu Yamada getting choked out by Bas Rutten. There are two interesting things about these examples, though. The first thing, you noted yourself:
A "superior" grappler can open themself up to an "inferior" grappler, take a risk, and pay a price for it. The second thing is that "grappler's chance" as we're discussing it here has a lot to do with surprise. Bas Rutten is a deadly MT striker. Did Manabu Yamada really expect him to lock up such a slick arm-triangle from the bottom? Same thing with Gonzaga Cro Copping Cro Cop. Gonzaga is a beastly BJJ guy. Did Cro Cop really expect him to throw such a beautifully set-up and executed high kick? The thing about a puncher's chance is more often than not surprise is not a part of the equation. Put differently, most puncher's chance examples will not be like Gonzaga Cro Copping Cro Cop. Instead, they'll be more like Goodridge and Rampage throttling Bernardo and Abidi: They knew that they'd be striking, but they still got caught because when you're swinging heavy leather, it only takes one mistake and one shot. With grappler's chance, by contrast, it's more often than not entirely about the element of surprise. You're on the ground and you're assuming that the person is thinking only defense, or just trying to get back to their feet. You're not actually expecting to go sub for sub, otherwise you would've been better prepared, you would've been on the lookout for that arm-triangle or that kimura or what have you.