i used to play a lot of doubles too. it was competitive but it was mostly for fun and relaxation.
and it did not do a damn thing for my singles game. volleying in singles is a lot different than volleying in doubles for one thing.
secondly you dont get to work on anything if you are a singles player. you DO NOT get the reps you need with your strokes, your serve, and your returns. you mostly stand around socializing. returning a few balls here and there does not help you work on your returns.
as general masterclass has suggested, even returning is not the same in doubles as it is in singles.
i would only play after all my singles activity but doubles definitely hurt my singles game. friends wanted to play and socialize and stuff so i would do it. and never did i bother with doubles in a tournament.
doubles works for certain players with a certain game but it does not work for most players who aspire to be great singles players. and that was mostly more tru in the past than today.
the game has changed now. singles is quite demanding. top singles players cannot afford to waste their time with doubles. it takes away the critical focus needed for singles.