I just write off Shin's amazement at Base Vegeta in comparison to SS2 Gohan or Babidi's estimations about the meter to simply be a typical inconsistency and poor writing.
I wouldn't say this completely writes off the suggestion at Pui Pui > Shin as an inconsistency though, since the argument for the opposite bar Shin's paralysis based on his performance against Boo are quite flimsy, especially when he also survived a battle with Manly GAINZ Boo long before with enough damage to show he did at least take a hit or two. Also, the Base Saiyan > Shin implications still continue with the Yakon fight even after Shin acting as though Vegeta was his first viewing of Saiyan power and the meter estimations had been rectified.