Bill, it's about cover density. Look at the stems of APW, see how far they are apart? Little fish need cover that is closer together, as they grow larger, the spaces between the cover can get larger and larger. My take on it is that 3"-8" fish can swim through that cover VERY easily, and smaller YOY fish don't have places to escape predation that easily, when compared to denser cover. Compare the stems of APW to plants like Coontail, Milfoil, etc. Not saying that THEY are good for a pond, just comparing types of cover.
Makes sense. I guess in my case, with effectively no submerged vegetation currently, I will take the pond weed, if it grows, as better than nothing.

I might try the Eel grass next spring as well if I can find a source.