Just some random thoughts. Thinking about this, we have to narrow this down a lot in some areas and broaden our vision in others. We are not interested in measuring how well they 'pass' or lob, if they are passing someone who chipped and charged to get to net, or someone who approached after a stroke or two or ten or fifteen. General scores or success rates against 'net rushers' are not what we want. Success rates on grass are not what we want.
Nor is 'big match play' on grass or carpet events quite what we want either. Matter of fact , I think we ought to look at early rounds consistency against a s/ver if players like Lendl or late career Connors, or a Leyton Hewitt might have trouble adjusting to or defending against the tactic in when they first see it at a Wimbledon Prep event, as well as looking later in the draw. That will not apply in earlier eras where could hardly be missed!
What about fellow S/vers who we seem to have excluded from this conversation. Maybe the real 'killers' can be discovered the break of serve rates of Budge, or Tilden, or Perry, or Laver, or a Rosewall from the wooden days in the 40's, 50's 60's and early 70's against other svers when a far higher percentage of matches played had two S/vers at war, and instead of a baseliner against a s/ver in the later 70's, 80's or 90's when there were fewer players and occasions to break such a service game .
Heck, maybe we are concentrating on the wrong Hewitt above thread! One of the best places to look is in doubles matches where s/v was the dominant tactic long past where it was in singles and on slower surfaces as well as fast! Great doubles and mixed teams by definition had to be fantastic at breaking down this strategy to win return games, even if they did it more with volley passes or lob volleys! The problem here of course is that you are measuring two players instead of one, but doubles will showcase a whole slew of nominees like Frew MacMillan, John Bromwich, the 'Woodies', Newcomb and Lutz, Roche or Jacques Brugnon, that otherwise would be missed.
Oh and by the way, lets not forget the women as we tend to ! Lets look at all the greats that had to break serve in an era with a lot of matches played in such circumstances and players like Lenglen, Wills, Connolly, Hart, Brough, Dupont, Hard, King, Court, and then maybe look at Evert or Austin