The mistake is his use of the word 'inherent'.
Judging by his edit, his mistake is he's talking from a point of ignorance and stating it like it's fact.
So let's break it all down. Which isn't hard to do.
"The wheel users have the clear advantage of not only greater control. When the car goes sideways from collisions or snap traction loss, much better chance of catching it exactly the way you want to."
No they don't. The one thing people say about switching to wheel from controller is that it becomes remarkably harder to catch a slide. This is because, in Gran Turismo 7, the controller has inbuilt dampening and 'assists' so to speak to make it a viable steering method because obviously, a wheel is not a joystick. Let's all keep that bookmarked, because we're coming back to it a lot.
"Ever tried playing assetto corsa on a controller. In any of the high performance road cars? Good luck. There's a not-so-obvious reason many play racing simulations on wheels. You're faster and more immersed in the simulation."
Yes I have, and yes there is. It's because in Assetto Corsa, there has been no work put into making a controller a viable input method. As you so correctly state later, a wheel is not a joystick (good job wheel, I'm very proud you got that right!) and therefore the game needs to adjust the inputs to put them at an equal level. Games such as Wreckfest, ACC on consoles, Forza and of course Gran Turismo have some form of dampening built in to gamepad inputs to smooth them out and make them viable.
It is nothing to do with immersion. Immersion doesn't make you faster. Silly point to include at all.
"Finally? Finally. If what you're saying was true. No cars would come equipped with steering wheels. Not F1 cars, not road cars. Just joysticks "because it's the same thing". Just no. They're not the same, will never be the same."
The only thing he said that's correct! Almost self aware here. It's not the same thing. At no point, did anyone ever say it's the same thing.
It is however, a game. And a game can do things that real life cannot. Such as put work into making a gamepad be balanced with a steering wheel by virtue of translating its inputs to better mimic that of how a car should behave.
"One has inherent advantages and differences over the other. Inexcusable."
Noone also said otherwise here. I even listed the advantages that a wheel has - and this is why a lot of high level players use them, fast cars like the X2019 do come up in GTWS and therefore to remain competitively viable on those combinations, a wheel helps.
The only inexcusable thing here is a clear inability to speak from facts, instead opting to yap about what they "think" is correct instead of taking a step back and realising that actually, Gran Turismo is a game so it doesn't matter what would happen in real life because you can do things in a game you can't do in real life. Their entire paragraph is a rant based around a single point they made up and got angry about, that can be disproven in one sentence. Incredible.