AG pools are only 3-4' deep so you will get even less temp difference. I really don't think it is going to matter. Also a second return probably won't give you much unless the pool is really big.

As to your last comment, AG pools are built for low cost and easy assembly, for the most part. Also, they tend to be smaller so don't need much extra circulation because they are round and avoid dead spots.

An IG pool can be built with a single skimmer and return (have seen some like this) but it doesn't take much more effort to add more returns and it can have large benefit because IG pools tend to be much more irregular so it is easier for dead spots to occur which can be alleviated by multiple returns. Usually they are done on the same side of the pool which makes it easier. Also, most IG pools only have 1 skimmer and maybe 1 main drain although the trend in the industry is to eliminate the MD. IG pools with two skimmers tend to be much larger pools >20k where the surface area is large and a single skimmer may not be enough to keep the surface clean.

So in general I don't think IG pools are over built because of the differences between the two types of pools. If anything AG pools tend to be under built because some of the equipment (e.g. Intex) is not really sufficient to keep the pool clean.