If bosses zipped around the place and were hard to hit people would complain about that instead and say "just nerf the auto reload perks instead and make the bosses less crazy!" It's much easier to simply nerf a few perks than it is to completely overhaul boss design from the ground up. The whole 'bosses are too stationary" thing has been making its way around the forums and Reddit for a while now. It usually takes Bungie 3/4 of a year to take gamechanging feedback and actually put it to use. The reason for this is because while we might be getting Shadowkeep soon, Bungie are already working on the next two seasons. Luke Smith said in the Directors Cut that we might not see an activity like The Menagerie or the Chalice for a while because they didn't know how well received they would be until it was out, and most of Shadowkeep had already been created by that point. Basically, my hunch is that we'll see some faster/harder to hit bosses probably 2-3 seasons from where we are now IF they actually use this feedback.