Overall winning % = 58
Doubles winning % = 57; comprises 3/4 of total matches
Singles winning % = 60; comprises 1/4 of total matches
So you're partially correct: my rating is 75% due to doubles.
But the only way you'd be fully correct is if my doubles winning % was a lot higher than my singles.
You can't get 4 games off of a one level higher player unless you had weapons [or they were goofing off or had a very bad day].
The flaw in this model could be if your 4.5 singles wins were against 4.5 dubs players who are not real 4.5 singles players, who just happened to be playing 4.5 singles (badly).
When that is the case, then one's 4.5 singles record is distorted.
All of this is the underlying premise that a 4.5 singles player is ex-college like Mark Sansait, who is my archetype of a real 4.5 singles player, the model we delusionally aspire to.
You know it when you see it.