My experience with Disarms is this: they are quite pointless. It usually requires one guy to disarm the weapon, and another guy to knock it away. But most of the time, the enemy have enough movement to walk to the weapon, pick it up, and continue fighting us.. It might trigger an OA, but that's about it. If the weapon is not knocked away, the target would just use free action to pick it up and continue like nothing happened. I can already picture him going like 'Meh, no biggie', every time he gets disarmed. I mean, 5e is already weird in the sense that having a weapon does nothing to help your defenses unless you have the Parry ability.
I think when picking up a weapon within 5 ft of an enemy should trigger an Opportunity Attack. Bending down to pick up your weapon puts you in a very vulnerable stance, and it should be a cue for attack.