Which you are welcome to do, if you want.
A troop of 800 orcs with a statistically average array of hit points attacks another group of orcs which is identical. Let us say that each orc in the melee has a 50% chance of hitting each round and each successful strike does an average of 4 hp damage each round.
The battle lasts 9 rounds. At the end of the battle, how many orcs remain with 1 hp? How many remain with 8 hp? For the sake of clarity, these are 1st Edition Advanced Dungeons & Dragons orcs armed with spears.
Alexis argues that he knows the answer, and that if you do not agree with him, you are really, really fucking stupid.
Well, Alexis' numbers look okay to me, I suppose, if we assume that the orcs all form a line and whack at each other until the weakest fall. But, then, what happens if the weaker orcs on both sides cower in the rear while the alpha males duke it out? Do we have any reason to imagine that weaker orcs are shirkers who hang near the rear? Only the source material, where Frodo and Sam are mistaken for orc shirkers in Mordor.
For all of that math to be relevant, it has to accurately model the variables of the scenario. Do you think that it does?
Okay, then, consider the possibilities of 1st level party consisting of a magic-user and 20 fighters. For fun, let's give them all maximum hit points per die, with no bonuses for Constitution. Which one of these fine PCs is going to die first? Should there ever be a 4 hp magic-user in a party? If we applied Alexis' math, and assumed that all 21 stood up toe-to-toe in a line with 21 equally NPCs, reason suggests that only the fighters remain. Of course, that's because PCs do not all stand up toe-to-toe in a line when fighting. Not if they want to live.
Likewise, I guess, we should consider thieves to be exceedingly rare in the campaign milieu. Monks, well, I can understand their rarity in a predominantly Western milieu, but they are another class that some players have managed to do quite well with despite their meagre hit points.
Wait! you say, that magic-user has spells! We must take that into account!
Sure. For one encounter. Then he is just a fighter without armour, with sub-optimal weapons and hit points.
There is nothing objectively "wrong" with Alexis' model, and you should use it if it feels "right" to you. But if it does not feel "right" to you, there is no reason to agree with Rumson just because "he knows".