Man, this hits home. I always topped my cuts too because that's what I was taught and it felt like the tidy way to do it, but once you stop and just let the branch collar do its thing, the tree heals so much faster. What really got me was how much less rot I started seeing a couple years down the line on the stuff I pruned that way. You basically stop guessing where the tree wants to seal itself off and let it handle the job. The hard part is just getting your eye trained to spot that collar, takes a bit but then it's second nature.