I think this is a great suggestion. There doesn't seem to be a good reason why dual-wielding should have a bonus that's much larger than the other styles with the new armor system. Tuning the bonus of dual-wielding down to bring it closer to the bonus received by the other styles makes those other styles more attractive, and also serves as a small step in closing the power gap between physical damage-dealing vs. spells. Also, given that I've seen quite a few voicing the opinion that PoTD is currently easy with an all-melee team, it would help to increase the challenge a little bit. Dual-wielding would still have the substantial extra benefit of full attacks.
On the other hand, I actually hope that there will be fewer ways to reduce recovery in Deadfire compared to PoE, and that reaching zero recovery without dual-wielding is essentially impossible. If you cannot easily reach zero recovery while single-wielding or using a two-handed weapon, then you don't need to worry that you're essentially just giving up 12 accuracy, a shield, or the bigger damage of a two-hander late-game if you choose to dual-wield.
(first post, so hi!)