do you practice exclusively with defensive ammo...
Shooting as much as you can, with any handgun, regardless of caliber or action type is the right answer for almost every non-expert. The .22 is the classic prescription for developing skill. Putting a couple hundred rounds per day through a .177 pellet gun in the basement could be the modern prescription for city and suburban types. And if one wants to master fast draw and always-accurate point shooting, a very large number of correct, consistent repetitions are required. In 2023, not many of us could afford to expend the tens of thousands of practice rounds that resulted in our McGiverns, FitzGeralds, or Jordans, especially if we had to use overpriced and overhyped defense ammo. All of those men, of course, spent many developmental years with the .22 and all of them recommended the same for us.
I also think that handgun hunting has quite a lot to offer the smart student of handgun fighting. Unlike the staged BS that pervades handgun hunting media, real shots on real trophies in real conditions have to be taken immediately - seconds or less. Bambi's dad will be visible and then gone if you can't decide and act and hit very, very quickly. We wouldn't use defensive ammo to kill a coyote, bear, pig, or deer, but it's 100% certain that anyone who consistently brings home meat every year is a better handgunner than any name brand professional instructor. Those abilities cannot be developed at the range, while many range-only skills are largely inapplicable to being able to hit moving targets in their small vital zones within a second or two in heavy cover.
To be fair, recoil, flash, noise, and hot cases ejected down your shirt collar do cause some shooters to flinch, develop bad habits, etc. If the good habits have become ingrained and reflexive via lots of practice with the .22, light wadcutters, or even the BB gun, those bad habits will probably not form at all. If they begin to form they can be easily addressed, particularly by switching to more reasonable ammunition.