barrel length has absolutely nothing to do with choke/pattern.
That's not true. It is true that with interchangeable chokes the length of the barrel has a lot less to do with shot patterns but back before those chokes guns were essentially designed to disperse shot by the length of the barrel. A shorter barrel (back then probably a 26") would be an IC pattern while a 30" would be a full choke. They had extra full chokes or the equivalent which would have been 32" or even 36" barrels. Those guns were duck hunting guns designed to reach out and take a large bird at significant heights. I know full well that first the adjustable choke barrel extensions (I have a Mossberg that has one - it's called a poly-choke) allowed people to adjust their shotgun from usually IC to full. Then came interchangeable chokes. But trust me, before those things existed spread patterns were controlled by barrel length. And that still applies to some shotguns. The physics still exist. They have just started using a different method for the most part but not always.
If you don't believe me maybe you'll believe Massad Ayoob
. Yes I looked it up but I knew this before I looked it up. I just went looking for proof of what I said. I'm curious though. Why do you think people sawed off their shotguns back when that was still legal? It was to make the shot pattern bigger of course. It has a limited effect but it does work to a degree. For example it won't hit everything on the other side of the room like they show you on tv but it will certainly make the shot pattern spread more than an IC shotgun.