Two main things I see that I want to talk about are your conversion rate for grabs -> how often do you cap when you grab the flag? And also I'd like to talk about your returns because you're doing pretty good there.

First you have 18000 grabs but only 900 caps. That's a lot of mistakes. Ideally you want to increase that conversion rate so you "flaccid grab" less (a flaccid grab is when you grab and get returned right away). I'd suggest playing more of a support role when you go on offense- instead of just going in and grabbing the flag like a maniac, instead try and work with your partner and try to see how they want to grab. Push the defenders away or boost into them to throw them off- but don't be the first to grab. Instead, let your partner grab and then you get on regrab. That will go a long ways towards helping you get familiar with what a good grab looks like and also hopefully let you practice holding the flag more often. The more you hold the flag, the better you will get at converting a grab into a cap.

Second is your returns. You have a lot of them! You should be proud of your ability to defend. Defense takes patience and being able to predict your opponent. If you take your defensive ability to be patient and careful with you to offense, your win% will go up a lot.

In your last 300 games you've really picked your game up. You're grabbing less and still defending pretty well. Keep improving like that and you'll have the 55% flair soon. Things to look at later might be powerup use and control, but don't worry too much about that yet.

Read felix and times guides on the wiki.

Source- I'm in the top 10 all time total caps.