Personally I'd prefer a "-X to hit" instead of disadvantage. The Advantage/Disadvantage system in PnP 5e is great for its simplicity, but an issue is that multiple sources of Advantage are entirely nullified by a single source of disadvantage (and vice versa). So if you already had disadvantage to attack, there'd effectively be no penalty for using these weapon abilities.
Since the computer does all the work for BG3, it's reasonable for numerical bonuses/penalties to be added back in.
