Your bike looks pretty good and has the right stuff on it.

With the quick release seat you can lower it on a dedicated down hill section and see if it gains any advantage for you. It would not be the whole course like you want as you will have to stop to raise once out of the section but it can give that feel. I think if you do this enough you will improve your descending skills which will translate to faster descents when your seat is in the fixed position. You can mix this routine into hill repeats.

you might want to invest in some flat specific shoe like the 510 brand there are many others. Having a positive connection with the shoe to pedal which flat specific shoes will do is a advantage. I used to ride clippless but have made the change to ride flats most of the time in the dirt

Fit is huge and you can gain power by having the bike fitted correctly small movement forward and back and up and down on the seat have allot of effect on comfort and overall power. go to this site
Bike Fit Calculator | Find Your Bike Size | Competitive Cyclist follow the instructions and fit your bike. Once you have this base you can fiddle with stuff and dial it in to what feels best for you

you can always do some things to dial in your current bike


I would mess with my tire air pressure ad find the sweet spot less can be more by running lower pressure your bike has more contact on the ground and this translate to smoother faster riding. Tubeless if you dont have it is a fairly cheap upgrade but you can always run the tubes at lower pressure as well

Same with your fork a few pounds of pressure one way or the other makes the fork perform suited to you as well as dialing in the rebound Lock out your fork on some climbs and get out of the saddle

Keep you bike clean and properly lubricated. conditions in the dirt are hard on a chain

The idea on sprints is flat out effort for 100-200 meters find a flat area rest just a bit between sprints and keep your heart rate up

On hill repeats mix up flat out efforts and easy efforts go in too big a gear and mash go in too small a gear and spin. Monitor efforts on a known quantity and find out gear and style gives you the best results

Do some sort of cool down at the end of each ride and stretch. Flexibility improves power

try to work out some routes with more climbing like double of what you are doing now.

Find a local club or group if you can. Ride with a group that is faster is always a good way to gain speed. Nothing like a bit of competition. If you see someone on the trial try to catch them and pass them if safe. If someone passes you try to get their wheel if they are faster just hang on as long as you can.

There is allot that can be done to get faster you will hit plateaus and maybe not able to break through them sometimes the game of trying is allot of fun however

Good luck