For me, it is the ships. I like all the toys and want to cram in the fanciest upgrades. I even played a Rhymer Redline cutlass build the other day.
Here is my example of what I'm getting at. Rhymer is goofy and frankly does not work in squad building. I looked at advanced homers and wanted to give him a go. So instead of doing what I assume is the "correct" thing, and picking efficient ships to add to Rhymer, I pick another ship I want to fly. Redline, now I know Redline and Rhymer together can't possibly work well together, but I wanted to fly the both of them so... I pick another ship. The cutlass with accuracy corrector.
I see this squad building method as basically inefficient. Rhymer should probably have very efficient squad mates if there can be any hope for him. But... There you go. That's how I end up putting squads together. They are not all this bad I swear!