I am the first to assert that there aren't many absolutes in the world of plants; however, from my own experience with bare-root pawpaws (which were field-grown) and from anecdotes all over the internet and "literature," I don't think root-sucker propagation with pawpaws is a viable alternative to grafting. The trees just do not tolerate such violence
When I first became interested in pawpaws and started reading about them a few years ago, I too read that growing pawpaws from root suckers varied in difficulty somewhere between impossible and nearly impossible. But, I tend to do things a little differently from everyone else and had discovered a clonal colony near my house, so I decided to attempt the impossible and transplant a sucker from that colony to my yard. Because I was impatient, to add to the difficulty I did this in the middle of August, in Alabama, the worst time and place to dig up and transplant anything. So, I went down to the clonal colony and selected the smallest sucker I could find, around 9" tall with six leaves. I dug a 2' in diameter, roughly 9" to 12" deep plug of dirt containing the root sucker. I immediately transplanted it into my yard, in a spot that receives full morning sun and dappled afternoon light. I watered it twice a day until the end of September. Despite the heat, it never showed any signs of transplant shock; it in fact showed the opposite and grew slightly in the next two months. I think there was such a large amount of roots in that large plug of dirt that it did not realize that it had been transplanted. That was in 2016. By the end of the 2017 growing season, the tree was 6' tall. By 2018, it was 9' and sending up its own root suckers 6' away from its trunk. It bloomed this spring, less than three years after it had been transplanted.
I have successfully transplanted two more root suckers from the original clonal colony since the first one, both in late spring/early summer of 2017; I did not retain as much dirt and as many roots with those two, and it seems that they "felt" that they had been dug up and moved. They grew very little for a year before starting to shoot up in height.
My point is that I believe that propagating pawpaws from root suckers can be a viable option and one that should be considered by more growers in the future. One of the benefits of growing pawpaws is that, with the exception of their habit of poor fruit set, they are problem-free: hardy, pest-resistant, vigorously-growing, and long-lived (as a colony, individual trees are fairly short-lived). I am not sure why some growers want to bollocks all that up by making pawpaws as fragile and finicky as the other widespread types of temperate fruiting trees.
Not to mention, you would have to go back to the original mother-tree for the sucker to be "on its own roots." Suckers from a grafted tree, of course, are clones of the rootstock, not the graft.
Agreed, you would have to go to original mother trees for these pawpaw varieties to get root suckers. Considering how recent the creation was for the most popular and acclaimed pawpaw varieties, those mother trees should still exist, in clonal colonies of their own making unless active pruning to prevent such colonies has occurred. Getting access to those trees might be difficult. But, if techniques for transplanting pawpaw root suckers can be perfected enough to create a viable market for the buying and selling of
au naturel pawpaw trees, then you will see it start to happen.
And I believe that techniques for transplanting root suckers can be developed and perfected. I have done it successfully, three out of three times. I guess I am too young and dumb to know that I was not supposed to be able to do that. But, imagine if someone who knows what he/she is doing worked on this method of propagation.