I think the biggest difference between Evert, Hingis and Sharapova was the influence of said 'tennis' parent. Mr Evert instilled in his daughter not a sense of entitlement, but a strong work ethic. Plus, Evert was treated exactly the same as her siblings which must have been quite grounding. And a sense of fair play - even if she didn't always like it: Mrs Evert often clapped her daughter's opponents and congratulated them on a win.Hingis got too cocky after her early success. She is underrated today. People say she could not win slams vs the big hitters but in addition to the 99 Australian Open she had numerous good chances (99 French, 2001 and 2002 Australian Open, to a lesser degree 2000 U.S Open, 2000 French) wasted of additional slams. Was really very unlucky and unlikely to not win atleast 1 or 2 post 99 Australian, if you break it down in detail.
If she had worked harder, not had her foot problems, and worst of all nto gotten complacent at the exact moment she most needed to step it up, she could compete with the big hitters minus peak Serena. That isnt to say many of them like Davenport and Venus would not be very challenging opponents for her, but she could challenge them. And peak Serena never lasts particularly long anyway.
The most impressive thing of all for Evert was her fighting back to settle the score vs Martina and play her almost even from 85-89, after being creamed repeatedly in 83-84. Most would have given up. That plus her determination in her early rivalry vs Austin when for awhile the much younger Tracy had eclipsed her, and was owning the head to head with her.
I agree if Maria had founds solutions in her rivalry with Serena she would be way higher regarded today. Obviously that was never the case.