That is simply absurd.
W-L record and PD are two things you have some control over. Who is in your league/conference you do not.
The non-champion promotion should be based on the data points a manager can control based on the strategic decisions they make (offense/defense strategies, GDP, TIE or CT, etc.).
Promotion should not be based on the bounces of the RNG determining who is in your league/conference.
The counterpoint could be made that your PD is also heavily influenced by the RNG determining who is in your conference (e.g., your conference had a team with a -769 and one with a -538, while the worst differential in my conference was -224. If it were even more imbalanced, and there were three teams giving up huge blowouts every game, it would be highly likely that the second place team in that league would have an inherent ~500 point advantage in point differential vs. one in a league with nobody actively throwing games. I think point differential is a pretty stupid tiebreaker anyhow, but at least in a single league it makes some sense because everyone in the division plays the same schedule (with the exception of home or away in some interconference games, perhaps). If there's going to be imbalance, I think the less injust system is one that at least rewards a consolation prize to a team that managed to win their division - which is, after all, within their control - rather than the one that puts up the highest point differential, which does in large measure depend on how competitive the worst four teams in your division are.
And if it's any consolation, I'm well known for having failed to promote to the NBBA numerous times when I should have, including a 22-0 season where I got swept in the finals after blowing a double digit lead when my key player picked up two technical fouls in a minute span late in the third quarter. I still don't know how the heck the game conspired to get me into promotion contention this season, but I presume that if your team is that good, you'll be up in my spot next season anyhow.