I agree in the real world, most people have one training pace. THAT is the big issue. For non-runners or new runners it's usually moderatly hard to outright hard. For more serious "rec" runners, it's usually moderate to moderately hard. Almost no guys over 20' are routinely running easy. That's incredibly rare.
You're acting like there is something wrong with running for 3 or 4 hours. Long run does not have to be 20% of weekly mileage, depends on the goal. One of the reason most of the hobbyists do 3-4 hr long runs is because of their basic schedule. If they want to run, say 60mpw, for there marathon. Most of them can't do 8M x 6 days with a 12M long run. 8M, easy, is likely 75-90' + showering, changing, etc. Lots of regular guys/gals don't have that kind of time. So...to get in the volume they go a bit longer, or significantly longer, on their long run.
Again, nothing wrong with this. 2+ hour runs have some significant benefits that other shorter runs don't have, particularly with regards to aerobic development, and especially when it comes to recruiting TypeII muscle fibers to work oxidatively. Again, go look at much of the research coming from Seiler. These are excellent studies looking at taking the training of high level elites and scaling it down to high level hobbyists or strong amateurs.
Of course, there IS something very wrong with all the moderate running that the typical hobbyist does. That's not helpful at all, and it's a main reason they are injury prone and not improving. Nothing, and this is found time and time again in studies of both humans and horses, leads to overtraining and injury as fast as monotony in training.