DandD said:
And why doesn't the 60 HD Balor who works for Demogorgon not simply overthrow Demogorgon? Or more precisely, the group of 60 HD Balors... Oh, and the 60 HD Balors would all have higher intelligence scores than Demogorgon would, simply through virtue of having more ability score modifiers.
In the end, just don't think about it, nor apply the rules as equivalent for real physics. They don't work. Not at all.
Instead of starting from the explanation, start from the result and work backwards.
1. We know Demogorgon is the big badass demon lord of the Abyss.
2. We know Demogorgon defeated the other demon lords to earn his station/reputation.
3. We can presume that Demogorgon has balors and other ultra-powerful demons among his underlings.
4. We know that Demogorgon is weaker as an individual than many of the other demon lords and certainly weaker than some of the ultra-powerful balors out there.
Now we cannot change things that are known. Those are our start points, those are the things that are given. Of the four points above the fourth is the where things appear to be incongruent, so if we are able to craft an explanation for the fourth that doesn't contradict anything we already know or is published in WotC canon, we should be ok.
Possible explanations:
1. Demogorgon created or oversaw the creation of the Balors and thus has a kind of power over them they cannot overcome.
2. Either due to creating them, or some other means, Demogorgon has knowledge of the ultra-powerful balors' true names. This knowledge ensures they cannot act directly against him and must obey him for fear of being destroyed.
3. In his conflicts with the other demon lords, Demogorgon was a superior tactician and strategist with more capable and effective demonic armies than his enemies.
4. Demogorgon in the past may have been significantly more powerful than he is now and his current lack of power is because he consumed so much of it beating the other demon lords. The other lords may or may not be aware of this, and if aware of it either don't want to advertise the fact they could get worn down too or don't want to risk expending too much of their personal power in a conflict they might not win.
However you elect to explain it, the fact remains Demogorgon has the stats he has (unless you house-rule it) and he has the position/status he has (unless you house-rule it). So rather than endlessly ranting about how it is impossible... figure out how it could be possible and get on with the game. Alternatively, if you don't feel like figuring out how it could be possible, either buff Demo's stats to where he could be in charge or write up some story about how the demon lord you think should be in charge kicked him in the nards and stole his lunch money.