In areas where I've had ~20ft aspen mulched, regrowth was sparse in areas where they were able to get into the ground a bit - I think from a combination of ripping roots out of the ground as well as building a thick layer of mulch on top that suppresses regrowth. In a rockier area where the guy was being gingerly with his carbide teeth and left a lot of taller stumps (looked more like a bush hog ran through the area... big chunks of tree and not fine mulch) the regrowth was significantly thicker/faster but the end product looked worse visually and isn't immediately suitable for a food plot or anything.
Best DIY regrowth I have found on the smaller stuff you are describing (at least with the majority of it being closer to the low end) is from winter cutting and leaving high stumps. I use a Stihl FS 560 in the winter, usually on snowshoes as I often have at least 1-2' of snow by the time deer season ends here on December 15th. I don't recommend doing it this way for safety/productivity reasons, but I try and stay out of my property until the gun season is over just so my resident does don't get blasted by neighbours. The pain in the ass with this method though is it makes a tangled mess of everything so unless I don't want deer to be in a certain area I have to go back in during spring and chainsaw most trees into 2 or 3 pieces so they sit flat on the ground instead of a 2-3' high interleaved pile of logs.
Here's a video from 2022 I recorded of part of a 3/4 acre cut I did with my 560. I did piece work pre-commercial thinning 15+ years ago (was also less fat and out of shape) and I'd estimate productivity would be 2-3x higher in the spring/summer/fall for just outright smashing down these types of trees. 4" would be a single tap with this saw to push over, 9" would require repositioning once to saw more around the tree. Stumps in this cut after the snow melted were 2-3 ft high, so I was constantly snagging my snowshoes, etc... blades stay sharper way longer though in the winter as not as much risk of hitting rocks and the bottoms of trees usually have more dirt content from rain/etc splashing it up.