Is it possible that your hand timed 400m splits are off by margins of over 3 seconds?
Something doesn't translate here--a guy running 50 flat with a 5 flat mile should be capable of around 2 minutes for the 8, probably just under. A 50 flat quartermiler with a distance background should be running well under 2 minutes in the 8. 50/4:46 should put you somewhere in 1:56 territory.
How many times have you run the 800? If only once, did you run it really stupidly (70-59? 52-77?). Have you won all your 800s by huge margins (5+ seconds)? Do you sit on leaders coming through 400m in 70 and not go till the final 200? 2:09 should not feel like a particularly hard effort for a guy with your 400 and 1600 capability.
None of what you've said makes sense tbh. No decent coach is going to let a 50 flat 400 guy waste his time running 4:45 miles on a regular basis when he should be running the 2/4/4x4 (and probably learning hurdles).
Everyone's commenting on your dropoff from 400 --> 1600, but a 50 flat quartermiler running 4:46 is not that severe a dropoff at all--that's what plenty of speed-based high school 1:56/1:57 guys do. 50/5:00+ would be a major dropoff, but you'd still probably be capable of 2 flat.
I hate to be so blunt here, but either you're doing something seriously wrong when you're racing the 800 or your sub 50 quarter speed is bogus.