Speed and endurance but not lactic tolerance

Perhaps you're just a pvssy?

"pure speed"

With a 24.1? Thats not fast at all. However if you never do any real speed work its not bad. What you might have is more fast twitch that you aren't training correctly. You sound like a typical 400/800 type training the wrong way (too much distance) and not enough plyos/speed and a little bit of the weight room.

Slow twitch fibers when it comes to speed are basically anything not type llb, and poor acidosis/high lactate are typical of type llb fibers, and faster type lla fibers. Likely if you're doing long runs and long intervals your slow twitch can be converted into type lla (through training) and your speed will improve remarkably over 200/400 and 800 with your endurance training.

Plyo's, real speed work, some weight room, maybe even weighted sled starts for the shorter distances. With serious speed work, if you can get your 200 down to around 22 flat while keeping a large part of your aerobic fitness your 400/800 should be good to very good.

key points:

real speed work is short reps 50-150m with total recovery

weight room focus should be on hamstrings/glutes

plyos should be in the 10-20 rep range focusing on R.O.M

all effort should be near maximal, and recovery should be complete

workouts with short rest aren't so "anaerobic."

Shorter sprints indeed produce more acid, and too much sprint training can be counterproductive for mid-d because you'll overdevelop type 2b/2x muscle that doesn't use oxygen.

There are two ways to beat acidosis - make less acid, or clear it faster. Concentrating on aerobic development at race pace does both. As muscle pH drops, more oxygen can be delivered to that muscle - and the hemoglobin that brings it there can then bind to CO2 and H+ and lactate ions to remove them. But if there's nothing in that muscle demanding that much oxygen, it doesn't happen. That's why "active recovery" works, and why you often feel acid after a race or hard rep, because you stop moving and its clearance slows.

The amount of oxygen you use on your tempo runs and long intervals is nothing compared to what you can use at race pace. If you don't believe this, wait till you're near what seems like the limit during your next tempo run, and then speed up to 800 pace. You won't be able to sustain it, but you'll be way above that "limit." That's what mid-D is about and it's wise to train accordingly.

Do you have any links to studies that show conversion of slow twitch fibers to type IIa fibers?