That argument has been posted hundreds of times regarding Federer: that you can't win 16/17 majors if your backhand is weak. I see the point -- as I see your point -- but I've grown tired of such arguments. If I criticize Fed's backhand, I am not claiming that it was too weak to win 16 majors. It obviously wasn't. If I criticize Rosewall's serve, I am not claiming that it was too weak to win 23 majors. It obviously wasn't.
It depends entirely on what you mean when you critique a stroke. I did not call Rosewall's serve a weakness. I said there were many alltime greats with greater serves; and I said it was far weaker than the very best serves. And that is true, and verifiable.
I also said it was not a "bad" stroke, because at that level there are no bad strokes. Rosewall, like Connors, directed his serve well, and it was not an easy thing to break him. But his serve was not a damaging weapon, as so many serves have been among the alltime greats. It's one thing to place your serve well so your opponent cannot easily tee off on your serve; another to lay down aces and service winners with regularity.
Even so Rosewall's serve has been attacked on big occasions. I do not agree that his performances in the '56 and '70 Wimbledon finals can be put down entirely to his having a bad day. Double-faults tend to come when the receiver is attacking the second serve; that is very common, at the top levels as well as among hackers. Rosewall was not the type to double-fault gratuitously in a match in which his serve was not pressured. Rosewall, probably less than almost all the alltime greats, was not an inconsistent fellow who had "bad" days on which he just couldn't get the ball in the court. His consistency was his great strength: which is why I think it's very sound and logical to credit Hoad and Newcombe for pressuring him into making those critical double-faults. It's far more likely that Rosewall was forced into those errors, rather than that he just had a bad day.
Here's what Newk did in that '70 final (Sports Illustrated):
Rosewall won the first set by breaking Newcombe's big serve in the 11th game and then holding his own.
But for the next hour it was all Newcombe. Whenever Rosewall missed with his first serve, Newcombe would take the weak second one on his forehand, perhaps the strongest in tennis, and pin Rosewall back on his heels. Newcombe won the second and third sets 6-3, 6-2 and when he immediately broke Rosewall to start the fourth set, the rout appeared to be on. Rosewall looked exhausted, and he would seize the brief rest periods to sit at the base of the umpire chair, waiting until Newcombe took his position on the court before rising.
Here's an article from 2006 that looked back on his great victory over Hoad at Forest Hills:
http://www.theage.com.au/news/sport/ken-rosewalls-1956-us-open/2006/08/25/1156012743457.html
Rosewall liked playing at Forest Hills because, among other reasons, the grasscourts' low bounce suited his less-than-booming second serve.
Incidentally that goes back to our debate about why Rosewall did better at Forest Hills than at Wimbledon: it was that low bounce at Forest Hills that protected him, to some degree, from getting attacked on the second serve. Laver hated those courts because of the low junk-friendly bounce; at Wimbledon (and Australia) the ball would bounce higher, and Rosewall's second serve would be easier to attack.
Anyway, there's no question that real damage could be done to Rosewall's serve. I don't call it a "weakness" for the reasons I explained above; but it was an attackable serve.
I find that significant because on serve, more than on any other shot, a player should be on offense.
The backhand is a totally different story. The backhand is where almost every opponent will attack you. It's where you should attack your opponent even if his backhand is stronger than his forehand, according to Vines. Budge had possibly the best BH of all time, and yet Kramer in their famous five-set match attacked it. Rosewall's BH was possibly the best of all time, and yet Newcombe served to it more than he did to Rosewall's FH -- as I tabulated recently; and he drew a lot of errors from it. That's just the standard play in tennis: attack the BH.
And that's partly why I question it when I hear that Federer has a weak backhand because it gets attacked. So what? Of course it's going to be attacked. Of course players are going to draw errors from it. It happened also to Budge and Rosewall.
Yet Federer's backhand holds up remarkably well overall -- except against Nadal's topspin. And in that regard we should remember that no one in tennis history has ever faced the RPM produced by Nadal. It did not happen in the wood era. In that era, especially at the grasscourt slams, Federer would have faced much lower bouncing balls; and his backhand is stellar against those kinds of shots.
His BH is the weakest part of his game but I can't agree that it's as weak, for a BH, as Rosewall's serve is for a serve. Federer can rip passes and other winners on that side; he can be offensive with it, and has been. Many greats in the past have been content to do nothing but slice their backhand (one example is Newcombe; I won't include Rosewall because while he sliced all his backhands, his slice was definitely not defensive!) Yet Federer can be do damage with his.
On the serve it's totally different. On the serve you SHOULD be doing damage routinely; you should be on the offensive. Rolling it in with accuracy is safe and fine -- that does not make your serve a weakness as such -- but there's far more that you can do with a serve, to damage your opponent. That's why I have never liked Rosewall's serve. His groundstrokes are far more imposing than his serve (I guess because he was a natural left-hander taught to play with his right).
.
