If you send Hayward instead of Horford, then you remove one decision-making agent. I.E., the only player who would have to agree to this would be Durant.
The 'negative' of using Hayward instead of Horford is that it would mean GSW would be taking on his additional year (player option). That's a legit negative.
That said, using Hayward instead of Horford is arguably better 'basketball' for each team given each team's roster makeup (assuming Hayward is fully recovered by next year).
And there is a chance that GSW could convince Hayward to opt-out and re-sign on a lower per-annum number next year. They'd at least have some alternatives to work with him as an asset.