I doubt anyone would argue we need another ACM, and I appreciate that looking at goals/assists from is certainly one measure of assessing who would be good.
I would say, though, that it's not necessarily the best measure of who fits that role - you might find that a quality attacking midfield regularly plays through balls or chips over the top to a rushing through wide man who then has a simple lay-off to the striker. The rushing through wideman and the striker get the assist and the goal on the stats, but if we're honest, apart from the wideman making a good run, the goal was created by the guy who played the through ball.
To put it simply - there's more to an ACM than goals/assists. I have to agree that Surman's assists, etc, don't look spectacular, but the fact is he was moved to a more central, deeper role where he would get less of those opportunities. But it's players like him who draw the opposition out and make space for others. Yes, maybe not the final ball or two, but Surman had an undoubtedly fantastic second half to the season in a team of (at the outset) questionable quality, in a position he wasn't really renowned for.
I still think we need another ACM, but having Surman back will make a world of difference. If by some miracle we keep Fer, I can see this sort of formation being extremely dangerous:
......................Fer
...........Howson ... Surman
Snodgrass......................Redmond
..................Hooper