Yeah, you're doing the typical bodybuilder type routine, don't take that the wrong way, there is nothing wrong with that, but it isn't very functional.
Depending on how much of a priority you are putting on lifting/physique vs functional strength/conditioning you may want to drastically modify your routine. I used to powerlift and compete in strongman, then after another back injury got back into mountain biking and specifically DH racing.
If I am lucky i get to race about twice a month from April/May thru October. During November-March I focus on strength, flexibility, and power 2-3 days a week and then I try and run 1 day a week, and circuit train 1 day a week.
During the season I start to get my cardio up (yes, cardio is important for DH) but not in the same way as XC, I need 3-5 minutes of pure sprinting, where as XC is a longer more spread out cardio.
Now I am working on Strength 2 days a week basically a push/pull upper body day and a Squat/deadlift day. Then I do as much riding as I can, and 1 circuit training type day. I aim for 15-18 sets, one week is high weight low reps (5x5's, sometimes 10 sets of 3, etc.) the following week I may do something like 3 sets of 50 (obviously i do less sets on these days)
Everything I use in the gym is compound movements, no bicep curls, no tricep extensions, everything is squats (front, overhead, sots press), push ups, deadlifts, push press, clean and jerk, snatches, Barbell rows, pull ups, etc. I also do a lot with Kettlebells, swings, cleans, jerks, turkish get ups, etc.
I have noticed that the functional excersizes don't allow you to push as much weight, but when combined in circuits or supersets really help with cardio and strength at the same time.
If you aren't willing to lose some size and want to continue lifting the same, you'll have to just be patient and ride a lot as your cardio comes up.
