So Venus is better than Maria because she has more Slams, yet Slam counts go out the window when it comes to comparing Maria to Davenport
Nope. As I always say when these discussions come up, if defensive abilities were just about who could sprint the fastest then James Blake would be regarded as one of the best defensive players in the history of the ATP - when in reality, despite how quick Blake was at sprinting from A to B, you were virtually guaranteed to win the point if you got him on the defensive - just like Venus (albeit to a slightly lesser extent).
Venus simply never had any clue how to play smart defence -- she'd go for winners even when stretched out wide, which resulted in a spectacular winner approximately 1 in every 10 attempts, but the other 9 times she'd either miss or she'd counter-intuitively be punished by hitting such a fast-paced shot, because it wouldn't give her enough time to get back into the middle of the baseline and her opponent would be able to hit to the other side before Venus could get there.
Maria on clay this year, even though her raw footspeed was a shadow of Peak Venus's footspeed, played just as efficient/effective defence as Venus has at any point in her career, because she actually anticipated her opponent's plays better and played much smarter defensive shots (mid-paced shots to a good length which gave her enough time to get back to the middle of the baseline and didn't give her opponent an easy putaway) than Venus has at any point in her career. I'd estimate Claypova this year won a similar percentage of rallies from when she was in defensive positions as Venus did (i.e. a small percentage). Again, it's no surprise that some of Venus's best matches have come when she's had knee injuries - because she has always lived and died by the strength of her serve and ballstriking, and her movement has always been irrelevant because it's never won her her matches at any point in her career.