-a ball hit not right at MIF will not get double play and winning run scores
-all infield in shrinks holes between IF's and any ball knocked down has a chance for force at home
The argument "for" infield in seems to make a stronger argument for infield at double-play depth.
- "A ball not hit at MIF would not get double play", but this ball wouldn't be fielded with infield-in anyway. And with MIF back, maybe it would get the double play (it depends).
- "A ball knocked down" with infield in might well have been a ball fielded cleanly (and double play) with MIF back.
And as you point out, having MIF back gives a better chance to catch short pop ups.
You didn't mention anything about the batter - was he a above average runner unlikely to be doubled-up?