It's been that way since D1--but here's the thing. Imagine if everyone had a slug shotgun or swords and rotated between the two for damage without risk of knockback or being physics'ed into a wall. The boss wouldn't be so challenging now would it? Slugs and swords are still amongst the top, if not THE best in DPS for pve activities and you can have loads of ammo reserves for both. But between stomping bosses and being forced to be more tactical than just bum rushing an enemy for an easy win, I'd rather have the challenge. Not to mention, it also makes ranged weapons more viable. Rockets are getting more usage this season, especially with their damage buff. I'd say stomping, as annoying as the mechanic is, makes the sandbox healthier, if only just a tad.