Alderweireld is more of a goal threat than either, realistically. Just because you're a wing-back that scores one screamer per season doesn't mean you're a goal threat.Walker and Rose have both scored screamers for us. They don't offer a goal threat in a back 4, with a back 3 they do though.
In a 5-2-3 they're playing the exact same role and position as they are in the 4-2-3-1. They're no more or less of a goal threat in either. Neither has ever been afraid to get forward just because we were playing with 2 center-backs before.