Agree there. I struggle because I rarely play doubles, and I don't take advantage of the extra width. However, whenever I've played a few days continuously, I can see a marked improvement. It's just that I like playing singles much more and the shots that seem to work for me in doubles (where I learn to take advantage of the extra dimensions) don't carryover much in singles. It might be different for others, where they can see that carryover effect much more.
Also, being extra aggressive, I am much more relaxed in singles, because win or lose it's on me. In doubles after a few errors, I tend to start playing not to lose because I don't want to let down my partner. It's not that my partner(s) is/are saying anything, but I start becoming more self conscious and more conservative. Even when my team wins those games, I don't get enjoyment out of it. Agreed that's a technique issue to hit with controlled spin that I need to get better at, but again, I'm just trying to explain why I personally don't enjoy doubles much. The way I play and run...I prefer singles much more and I also feel overall it's the more challenging version. Looks like many on this thread disagree. That's fine. It's my opinion and I could well be wrong.