My bad, I thought you were a pilot from other threads.
I ran the same distances; I also paid attention in physics.
If you were cranking out sub 5-minute miles in junior high, then you should've stuck with it. Regardless, I can guarantee you weren't anywhere near 240 pounds when you ran those times.
As for your comments about the decathletes not having much body fat and therefore not at much of a disadvantage, I'll reiterate that you are ignoring some very basic physics. The amount of work that Leo has to do to move his 240 pounds around the track for nearly four laps is vastly more than a 1500-meter specialist who is 100 pounds lighter. Honestly, I'm not trying to be a jerk, but your argument is staggeringly ignorant.
As for the "front guys being competitive," uh, yeah, there's a reason for that. Niklas Kaul, who won the 1500m decathlon event, weighs 198 pounds. Those ~42 pounds make a massive difference, regardless if they are muscle or fat.
Then, you have to factor that this is the final event out of 10 after two grueling days. That is also going to have an impact on their times, although not to the degree that their weights will.
(Btw, sprinters tend to have lower body fat % than milers. Total mass is less of an issue in a sprint because it's an inefficient energy dump, but once you get to the middle distances, the need to be efficient over time becomes paramount.)