Yes I do agree on all of that. Navratilova and Evert were so great and so dominant jointly they snuffed out a lot of the belief of the younger generation of players, probably even moreso in the US. Well I wouldn't really include Turnbull in that as she is older than both, I think she was just never going to be good enough, but would apply it to those others you listed atleast as a hypothetical. And getting the experience of playing big matches early on is super important to your mental development to having any chance to become a champion.
And yes that is why I think the grass field back then was stronger than the clay field since players games were built to play on grass, even moreso in the 70s and 60s when the grass field was stronger than the 80s, and when there were many more grass events than even the 60s and 70s; hence why I say Evert who shone greatly in the 70s, much moreso than Martina, had the stronger grass field of those two. I think the strongest field in the 80s was actually on carpet, which makes sense as that was the pre eminent surface probably, with grass slowly being phased downwards, and hard courts just starting to become more prominent. Players like Hanika, Kohde Kilsch, Shriver, Sukova, Austin, Jaeger, some of those who aren't even known for grass which is considered similar to carpet, and the obvious 3 of Navratilova, Evert, Navratilova, all had some exceptional performances on carpet. That makes Martina's feat of 8 (?) I believe YEC on carpet all the more impressive, and in some ways even more impressive than her 9 Wimbledons IMO despite being less prestigious. And then in the 90s when Graf played there were barely any grass tournaments so it makes sense the grass field would be relatively weak, and the strongest fields during Graf's day were on clay and faster hard courts, which makes sense as those were the surfaces that featured on tour most. Players are the product of their surroundings.