I think that's a bit of a shortsighted view on how you factor in effect. Yes, they both set the bar incredibly high (best loanees we've ever had IMO...) and yes they both contributed in two very noticeable ways - tightening us up at the back, and bringing goals and creativity at the top of the pitch.
You could argue we have a little of that now (in Wes' form last season, long may that continue) and we clearly need creativity up top and MGW would be beyond difficult to replace.
However, Choudhury would address another key area, shoring up central midfield, adding legs, energy and bite. Leaving us less prone to being turned over in midfield and less vulnerable on the counterattack. Our Achilles heel. His output would be less notable (clean sheets, goals) but his contribution would be to the system and you know we'd be the envy of every other side in the division if we were to get him.