Evert is underated on grass. Several of her strengths lend themselves beautifully on grass. Combine her strengths with hard flat strokes and you have a big problem on your hands.
Her game was extremely efficient and grass rewards efficiency. Her strokes were economical - no big backswings, nothing excessive. Her movement was efficient - each step purposeful and rarely caught out of position.
Her anticipation partially diluted the speed of the court. Evert wasn't as fast as Graf but no one was quicket to recognize where the ball was going.
And then there was her mental toughness that counteracted the bad bounces. If she's getting bad bounces then so is her opponent. Evert didn't like it, but she refused to show it. Her body language suggests to her opponent "I can deal with this, Can you?"
Australian grass set Evert up beautifully with its higher bounces. Remember, she never once failed to reach a final there.
The one true weakness Chris had on grass was an attackable serve. But so few could actually make her pay.