I gotta say, I don't agree with this, still. Kerry King hit his 800 with a Tube Screamer and a 10 band EQ and his tones were still fairly dry in comparison to modern tones.
I get told on my Youtube videos all the time I need to use MORE gain, but I disagree with the guys who say that as too much gain muddies things up, especially in a mix. In saying that, a stock 2203/2204 isn't enough for me with an SD1 or TS9 out front for my tastes, which is sort of modern thrash and 90's hardcore/crossover stuff.
To each their own, and I respect your guys' opinions, I just can't say that I feel the same about the level of gain these amps can achieve, stock, with a boost out front.