if you start in d4, you have to be teh top 6% 3 times, a HUGE ask. (ignoring lucky autopromotees with great records)
You are absolutely right, but it can be done. I started mid season 4 and have won 2 championships and made the semifinals the 2 seasons in between. This season...I think that I am running a borderline playoff team.
You made me go look it up. In our league, there are 7 teams starting in season 2, 7 teams starting in season 3, and 2 starting in season 4. I'd say that at least some empirical evidence backing us up that starting earlier was an advantage.