The original 'discussion' was on whether old style can compete against modern style, so I guess the baseline assumption is the players from the old days, pre-2000s, would bring the exact same game they played in their times. Do you honestly believe they could compete successfully against modern players in modern style? Navratilova, as great as she is, would be easily passed by the modern players whenever she comes to the net. Graf's BH will be attacked and get broken down like Federer's BH was broken by Nadal on clay. Seles essentially had similar style to modern players, but she would be matched and even overpowered by a lot of modern girls...
Yes, I absolutely believe that, and I'll tell you why below...
Ibut those are more modern players who set a new trend in women's tennis - Hingis, Capriati, Davenport, Williams sisters - they are the beginning of a new era in women's tennis. Older classic generation ends with Graf, I think, and Graf was great and is actually my favorite female player of all time, but I have to admit her style wouldn't dominate the field today like she did back in her time. Of course, if she was 20 years younger and learned a modern style tennis with two handed BH and all that, it would've been different, but her style was more for her time. Serena's prime was actually in the mid-late 2000s-2010s, so I would call her a modern player.
Look, a lot of these arguments are based on feelings or interpretations, but as
@AM75 pointed out, we actually have some hard evidence to go by. First and foremost, people tend to forget (or not know), and maybe you forgot, that Graf actually played both the Williams sisters, and on several occasions. The H2H's are either equal, or slightly in favor of Graf vs Venus (depending on the source), but we can call them equal for arguments sake.
And we know that this was a physically depleted Graf who's body was starting to break down, against young Williams sisters who probably still weren't at peak level. So that probably balances out, no? Anyway, the point is that Graf very much held her own against these two "modern" players. Good old Steffi, with her older style racquet and slice backhands had no problem handing the power of the Williams sisters (because they were already powerful), and the Williams sisters were NOT able to attack and break down Graf's backhand. Not even close.
Also, as
@AM75 pointed out, Navratilova was able to keep playing doubles until a ridiculously late age, so we know her net game holds up to modern players and equipment just fine.
For further proof, we can look at comparable modern examples, the most glaring of which is Ash Barty. So where should we begin? How about Ash's backhand? She sliced a lot, and it was a slice that, at best was comparable to Graf's, but in reality wasn't nearly as good. And did players attack and breakdown her backhand? Nope. And before you argue she could fall back on her 2-hander for topspin shots, Barty's regular backhand wasn't remarkable, and certainly not the weapon that Steffi's one hander could be, most notably when she would create amazing angles with it.
How about Ash's forehand? Not a power shot, just consistent and accurate. Something Graf (and others) would have no problem matching. So let's talk about Ash physically: she is short, and while she is indeed athletic, she was nowhere near the sheer athleticism of Graf and Navratilova. Both of them were significantly faster than her, had better footwork, and were taller to boot.
And what is the point? The point is that Ash was #1 in the world, practically playing part time, and probably could have racked up a bunch of slams if she played with the regularity and drive that Graf and Navratilova showed. So...
One last thing, on Martina and playing S&V in the modern game. Again, we have a little bit of evidence to work with. Remember when Taylor Townsend used S&V almost exclusively to make a shock run in the USO a few years ago? Yeah, that's Taylor Townsend, a player that is about 1/5 as athletic as Navratilova, 1/10th as good at volleying, and 1/10th as good at serving. Because yeah, Martina wasn't just rolling her serves in wherever and rushing the net, she was placing them extremely well, something that is basically unheard of in the modern WTA tour. So nobody was going to be passing her with ease. Most of these modern players can't even pass off a sitter of an approach, or a pancake second serve, so they aren't going to pass Martina when the approach is sliced down at their shoelaces and they know Martina is a monster at the net.