I think Martinez would like to give a back 3 a proper long term run at some point and I think Galloway as the left side of that 3 is what he sees as a real viable option.
I was unconvinced by Galloway at the back end of last season, as to whether I saw a long term future at the top there for him. That's changed this season. He's looked so comfortable. I honestly believe had he not gone off injured, we would have held on to a 0-0 against City.
All this said, what Baines offers us going forward/from set pieces/as a general attacking outlet, I think against the vast majority of teams we need to pick the stronger attacking option over the stronger defensive option.