Requiring the use of an Action to "re-equip" a disarmed weapon you have picked up from the ground with your free item interaction isn't expressly part of the D&D 5e rules, but there are a lot of "homebrew" adaptations Larian has made for the game (which is overall fantastic imho) and as long as they are consistently applied (and they seem to be), I'm here for it. That said, allowing an enemy to disarm me, pick up a legendary weapon I spent an hour solving a puzzle to acquire, and effectively make it vanish because they do not leave behind a lootable corpse is neither "realistic" or fun. I ended up just cheesing the encounter to avoid having to fight an enemy with Disarming Strike as they kept taking my best weapons. Feeling like I have to cheese an encounter to avoid unfairly and irrevocably losing something I worked to obtain feels bad. Overall, the game is great, I just wanted to leave feedback about this one specific instance of "feel bad".
I haven't encountered this yet but I've seen the complaint enough that now I dread it happening. I try not to be too married to most weapons but when you get that ONE thing that feels like it completes your build and then lose it, that sucks. I'd be okay with 'he grabbed it and then I blasted him off the cliff' because that's on me, but to have it vanish and his lootable corpse is right there or they die due to a cut scene and take my stuff with them? No bueno.