Gaara is overrated...he got pressured hard again Madz while people considered to be weaker than him outperformed his hype in that fight. So I agree.
I don't think Mei os over or underrated. She's rated fairly from what i've seen, she's not particularly bashed or overly loved.
Sasori suffered from being early game enemy, Sakura did not solo him. His loss was reasonable and in the end indeed threw the match. He was pushed to that point by all means I believe this but he could have won that fight high diff..