Depends on how much delay the other person has. If it's a lot and the server is lagging, it becomes quite annoying. Once you know when to hit, it's pretty easy. Going from fighting a a delayer to a non-delayer, then a lagger forces you to adapt too much. Add the server lag in, and a lot of the time you have to change your timing multiple times in just a single match.
When there aren't many people on though, around 2k or so, it's pretty easy to beat any delayer, if you know what you're doing. All I can say is that, you will win more consistently against anyone, if you spar enough.
If anything, delay is a disadvantage to how good you could actually be in the long run.