You are not a 4/8 guy. you are a 8/15 guy who doesn't want to do the work for it. Your differential is 5sec from 400 to 800. You may not be training properly for a 8/15 guy, and at your age you are going nowhere as a 4/8 guy if you can't break 50sec for 400m anyway.
I coached a guy the past couple of years (turn 19 this year) who also thinks he is a 4/8 guy, but really isn't either. He runs sub-48 barely, sub-1.47, has only run one serious outdoor 1500 (3.45). Ran 1.47 in HS off no more than 25 miles per week. What is your 200m best? if it isn't sub- 23.0 (or faster) don't delude yourself. You need better endurance AND better speed (increased strength) or you will be plateauing very soon. But that still doesn't make you a 4/8 guy.
Off a 1.50/52 (49sec 400) this kid couldn't have run under 4.20 either, until he actually started to train properly. For all you know you could be similar - I made him do XC (only a couple of races) to engage him in the process of getting fitter, while doing stairs and hills to get stronger. Guys who could beat him by 2-3 minutes in his only previous XC race, only beat him by 20-30sec after this base.