Pat, your numbers are wrong. There are plenty of courses that start on par 3s. All the ones I'm familiar with have 10 minute intervals, at most. And they maintain them just fine.
Sure, it might occasionally take a group 12 minutes to play the hole if they have extenuating circumstances, just like a group teeing off on a par 4 might lose a ball, search for five minutes, come back to the first tee, hit again, and take more than 12 minutes total to clear the landing area. But in real life, it doesn't take over 10 minutes for the average group to play a par 3 opening hole.
Can you name three courses that start on a par 3 with a tee interval of over 10 minutes? Or three that have regular difficulty maintaining such an interval?
I suspect you don't have much experience on crowded courses on Saturdays and Sundays if you think groups teeing off on a par 4 always wait the full tee interval before hitting as opposed to wailing away when the landing zone clears. If a group waits the full interval, it doesn't really matter much what the starting hole's layout is from a pace of play standpoint. But in the real world, where groups often don't wait the full interval and hit when the coast is clear, a straightforward par 3 opening hole has real pace of play benefits that can't be denied. Maintaining the full interval is the real key, and a par 3 opener virtually assures that this goal is achieved in a way that par 4s and 5s can't. Starters and rangers can also accomplish the task, as can intelligent players. But those are not architectural features.