That's a really bizarre comment considering that one big point of 3.x was that they unified monster creation so there were rules for it all as opposed to earlier editions where you just made up numbers and compared to other monsters to guess how tough it was.
You know, I had this exact same argument back in like 1993 over 1e AD&D. This is really old ground for me.
So, before I get into that history, let me say you are entirely wrong in all of your assumptions. There is no unified monster creation in 3.X. There are no rules for it. And that wasn't a big selling point. I'll explain what there was in a bit.
Back in 1e AD&D I once got in an argument with a player who claimed that I as a DM was breaking the rules because the goblin tribe that they were fighting didn't have the demographics outlined in the 1e AD&D monster. The player argued that they shouldn't have to fight 5HD goblins because there was no such thing as 5HD goblins. The player claimed that I was cheating to give them weapons not found in the write up for goblins, or to give them leaders not found in the write up for goblins. I pointed out to them that TSR's own published works, including the works of the same person responsible for the monster manual, did not in fact follow the demographic "rules" in the monster manual because they were not in fact actually "rules".
This is pretty much the same argument. You've mistaken guidelines and tools meant to aid and empower the DM for a set of rules that bind them. There is no rule that there has to be 13 encounters for each level. There is no rule that PCs have to have their suggested wealth by level. There is no rule that 20% of encounters need to be of a certain CR relative to the parties ECL. All of that discussion of the underlying assumptions of the game system isn't there to create rules, but to help DMs understand how the math works and to understand the consequences of certain decisions, and to help them stay in 'easy mode' until they have the understanding to follow their own creative impulses.
It's almost like people are blocking that there were specific rules for foe creation, that followed the rules for character creation, and this was a big difference from earlier (and later) editions.
I'm not blocking out anything. I remember when they published those guidelines. But there is a huge and insurmountable problem with your argument that there were "specific rules for foe creation", and it's pretty much exactly the same problem that the player back those nearly 30 years ago was overlooking. If in fact those are "specific rules for foe creation", then there is an insurmountable problem - the monsters in the Monster Manual cannot be created from them.
Pick just about any monster in the Monster Manual and it defies the so called "rules" in one fashion or another. There are in fact no rules. The writers of the monster manual didn't limit themselves to some rote mechanical creation system, likewise the DM is not limited to some rote mechanical monster creation system. They can do anything they like, and none of it violates the rules.
Don't believe me?
I can assign a racial bonus of any size I like to my creations. I can grant any sort of exceptional ability I want to my creation. If I want to create a monster that has the Exceptional ability, "Tougher Than Usual (Ex): This monster has 120 additional hit points.", I can do that because there are no rules, no limits, and can be no rules and no limits for what abilities that a monster has.
So are using what was done in other editions - that worked better - but explicitly was not the rule in 3.x - to try and say that the rule in 3.x was fine.
It's just not a rule. There is no rule that says, "If you have a ship's captain you can't just write, "Fighter 7" or (F7, Str 16, Profession (Sailor): +16, rapier +1) beside the entry and be done. You have to stat out ever skill bonus and every feat before hand." There just isn't a rule that says that. There is no rule that says, "Gee, if you've not got a stat sheet handy for this NPC and combat breaks out, you can't make an informed guess of their likely to hit bonus. No, you have to do a bunch of work that isn't relevant to the encounter." There is no rule that says that.
You're just making things up, like the guy that said, "You can't have 5HD goblins. That's impossible."
And the more people say "don't bother with this rule. just fake it", the more I will continue to point out that is not support that the rule worked correctly and was not broken.
The guidelines worked pretty great. They did work "correctly" (whatever that means). But you didn't have to use them. They were guidelines. They were a great tool chest. But, you could make not only whatever you wanted out of them, you could just make whatever you needed.