Maxwell is not the potential match winner you are looking for. Even Jake Lehmann has better figures in the Shield this season.
He is not in the top 10 batsmen this Shield season.
Maxwell: 2 matches, 4 innings, 126 runs at 42.00 with HS of 57. 0 hundreds, 1 fifty.
S Marsh: 3 matches, 6 innings, 443 runs at 88.60 with HS of 163*, 1 hundred, 3 fifties.
At least S Marsh was in the top 10 in the Shield for the early part of the summer, so were Harris and Handscombe. Given how badly they have struggled against India I doubt Maxwell could do any better starting off on worse form. The level in quality between a Shield attack and top shelf test attack is so great that anyone even slightly off will be found out.
A lot of hypothesising and selective reasoning there.