My dearest apologies for expecting that you could follow along with a sentence structure slightly more complicated than what one might encounter in the seventh grade.
Yeah; that'll be it.

To the contrary, I would say that's exactly what makes it different. Thesz was concerned with only the act of wrestling itself, i.e., presenting a staged fight that looked real enough for the audience to believe in it. Modern wrestling (say, post-Hogan) is concerned with the overall narrative structure and only uses the act of wrestling as a means to an end. It's the difference between the act of painting and the resulting picture. For Thesz, the art was nothing more than painting. People were showing up to watch Da Vinci slap paint on canvass, and abandoned it as soon as Da Vinci decided he was through painting. Modern wrestling is more analogous to going to the Louvre and admiring the Mona Lisa. No doubt there's interest in the means by which it was created and a certain admiration for the technique and mastery involved, and only an artist of great skill could produce a masterpiece, but the most important factor is the end result. Thesz and modern wrestlers work toward two entirely different ends, on the artistic level, anyway.
So I'm just going to go ahead and try to bypass as much of the nonsense about painting as I can - it's an utterly nonsensical metaphor that bears no semblance of relation to what we are talking about - or perhaps my seventh grade brain simply cannot handle the complexity of your thought again.
Thesz and modern performers both work to precisely one end, which is the entertainment of an audience. That is all the professional wrestling has ever been about; you can blather on about the "artistic level" all you like, but all that Thesz, Sammartino, Hogan, Austin and Cena are doing is staging pretend fights aimed at entertaining an audience sufficiently that they will be willing to expend money on seeing it. Not only is Thesz one of the best at doing this in history; he also invented, pioneered or popularised half of the techniques that contemporary talent use today.
The fans in Thesz's day wanted a more realistic product so that is what he provided. That is the only difference. If the fans had wanted contemporary wrestling then that is what he would have provided, as is proved by his time on the East Coast and in Mexico. (Go and check out Thesz's matches with Rocca and Sammartino and find me a single way in which they differ from contemporary wrestling that can't be refuted by comparing Hogan and Mysterio and I'll drop out of this debate right now) If Hogan's fans has wanted a more old school and realistic product then that is what he would have provided; and is similarly proved by his time in Japan.
There is no fundamental difference between the two.