It doesn't matter. LOL. Amy only needs five more rings to put you in another one. I could take real shortcuts on Shadow stages and Amy would still win simply because she only needs 5 rings to put you in a time stop. Sure, it may only take ~3-4 seconds, but in that time Amy can easily get another power-up and put you in another one, and if the Amy plays smart and never hits a checkpoint and kills the opponent, then it's done after one death because Amy'll continue to get 5-ring power-ups. I was like you and thought Amy wasn't THAT bad... but then Zwarm and I played. LOL.
I'll never do a Vs. MM in SA2B. I would gladly do a speed run MM, tho.