Personally, I'd hope for a more literal and visual interpretation of "Feed on you", maybe involving a giant tongue coming out of their moth and them consuming the dungeoneer... But it's a death I'd have liked to see.
At least one of the blockers was given a chance...
Igneous should have eaten Akash, by all rights. Although he'd have been more of a mid-morning snack than a whole meal.
It would have been good to see what happened when someone got all three wall monster riddles wrong - as you say, Akash should have been eaten by Igneous.
I wonder if they just didn't have the technology at this point to show us the result. It would presmmably have looked like Christopher's death in series 5 at the hands - or rather jaws - of the blocker.