I'm not sure how they got to that conclusion, but we can kinda guess.
The tongue is PACKED with blood vessels, so in case of any damage it can get tons of nutrients to fix itself. But this takes a very energy-intensive.
So if the rest of the body would have the same density of blood vessels, we'd need drastically more energy to feed all of that.
And I guess they're asserting that all else being the same we wouldn't be able to ingest or process sufficient food to keep that going.
It's a bit of a strange argument though, I'm going far outside of my physiology understanding, but you'd have to imagine that had we evolved such advanced healing capabilities, we'd have also evolved the means to feed them. And OP underestimates just how much food someone can eat. As someone dealing with an ED, I can tell you that you can easily triple your calorie intake (though whether that's sufficient I wouldn't be able to say...).
All in I'd look forward to OP defending their assertion.
That could be any American re-entry capsule since the apollo era, including the Boeing Starliner.
But it looks distinctly not like SpaceX Dragon 2.