Interesting about Roddick and maybe the reason why Stefanos isn't able to be more effective on these metrics than Roddick is he holds back on the forehand, which Roddick didn't, at least not while he was with Gilbert. This is a problem that both AZ and Stef have; their forehand doesn't hurt enough. Stef's netgame gives him a dimension that AZ doesn't have but it's not enough in the modern game.All very true Tsits's best prospect is to develop a serve better than Federer and Sampras (sounds all too much like Roddick) and couple that with Sampras clutch returning. The issue for Stefanos is he may be clutch on return like Sampras, but his overall stats are very likely to be on par with Roddick. Stefanos doesn't have a game that feels like Roddick's, but the numbers say he'd be lucky to have Roddick's prime stats.
All you say is true, but a bigger serve for Tsitsipas might get him the upset of the Mad Lad there and there. If he's able to hold serve against Medvedev he's very much in the match.
Goatsipas just turned 21 so we don't know for sure his ultimate return level, but we can be assured he's no Djokoray returner or even a Mederer at this point.