Well, there are a difference between good heavy bags vs horrible ones out there. That's mostly in the quality stitching, stuffing material (and especially how they stuff it), as well as the bag material.
But you are right about you don't need to over-complicate it, you don't need Italian Leather that Grodex prides on or even Superare's FRYE Leather (the $10,000) Heavy Bag. Especially since you're buying a heavy bag to punish the shit out of it. If I had the cash, I rather buy a very plain Winning Japan Polyester Canvas bag that is easy to maintain and is built to take damage. That's one of the reasons they developed their unique Polyester Canvas instead of using leather (even though their leather still holds up pretty good, picture below). Not to mention, from what I see from pictures that my friend showed me, Winning Japan has a very good way of stuffing their bags that even after long use/hang, the material doesn't settle in the bottom. The middle breaks in a little from hitting, but the stuffing on the top doesn't sink into middle and the middle packs in the bottom making it like concrete.
However, I gotta give Grodex's innovation by tackling the top bag squeeze problem with a metal ring to spread out the weight, time will tell with their bags to see if that really work since it's gravity and you can't really avoid it.