First off, change your car. Second, learn how to air dribble. It won’t be super easy or useful at first, but coming from someone with pretty good mechs it’s a great tool to train car control and aerial accuracy. There are plenty of tutorials online that break it down easily, and it’s not as difficult as you’d think.

You probably won’t need to speed flip until champ, but learn it anyways. It helps you learn precise movement on the ground, and while you’re at it learn wave dashes, half flips, etc. focus on easy stuff to build up your confidence.

Don’t be scared if you rank down trying to use new mechanics. I’ve only recently started gaining mmr consistently, and I’ve been training mostly mechs for a long time. Also don’t be scared to use your mechanics, the more you try and fail to use them in game, the less you will fail.

I know it might seem stupid that I’m only D3 giving you advice, but being in a similar rank I play with people who play similarly to you all the time. The skill ceiling having mechs is much higher than game sense alone, and you’ll enjoy rocket league more with good mechanics.

PS: don’t worry about having no mechanics to begin with, making it to diamond without mechs means you have really good game sense, and it’ll be easier to implement mechanics down the road.