Evolution just means change, not improvement. The biggest shifts in tennis were caused by changes in the tour, specifically the business side of tennis: corporations imposing on the game alterations that they feel would make them more money. Since the Open Era began, players have done their best adapting to rapidly changing circumstances outside of their control. Those who adapted best in the 70s and 80s were those who were most entrepreneurial, always looking for the next thing (equipment or otherwise) that would give them the advantage. In the 1990s this was largely true as well when early adopters of poly strings saw the best results.
Since 1990 the tour has largely standardized, partly to give the players a less hectic experience, and although there have been changes they have been less drastic than in the 70s and 80s. Since the early 2000s (when the poly strings were widely adopted), the game has changed relatively little in terms of style and matches look mostly the same. The game's best players in the last two decades have been the big beneficiaries of this "quiet period" of the past two decades: Federer, Djokovic, Nadal in particular -- none of whom have had to wrestle with much upheaval on the tour, while also benefitting from the homogenization of surfaces. Their longevity and continued success owes much to these circumstances.
The "organic evolution" perspective is a banality I don't subscribe to. Nothing about professional sports is organic. The bigger side of the game is the business side. Most change happens due to corporate-economic circumstances and is spearheaded by wealthy business interests in dialogue with other governing bodies and players. Tennis is becoming more change-averse now and things are more stable and consistent for players. 20 years that passed between 1973 and 1993 felt like a massive amount of time. Conversely 2003 to 2023 feels like relatively little has happened.
If you look at other sports, you'll see the same patterns. A conservative tradition-oriented sport like baseball, particularly Major League Baseball, doesn't undergo major changes like tennis did, the sole exception being the steroid years (which were since curbed). But otherwise the equipment has stayed the same: bats, gloves, uniforms. You can imagine Mickey Mantle still dominating today. What he did with his bat in the 50s he'd still do today. The nature of pitching has changed, but that's largely due to coaching philosophies about the risk of injuries and the economics of paying $200 million to a guy who might blow out his arm tomorrow. But the game has been pretty much the same for decades upon decades. No one today runs faster than Rickey Henderson or hits the ball harder than Babe Ruth. They could switch to aluminum bats tomorrow and players will hit many more home runs and you can be assured someone will claim that this is proof of "evolution" and players getting bigger and stronger because they're drinking special milkshakes or some nonsense like that. The real big changes are corporate-economic. The NBA also changed in the past three decades, becoming a less physical rough-and-tumble sport, and one more focused on long-range shooting skill, and this was all done by design by the commissioner and the corporate interests at play because this was the business model they wanted. The business side of sport is what changes the sport.