The Charizard is the epitome of pokemon dominance and masculinity.
Let's start by looking at his body. His body is large. His domineering size makes his presence known without him even needing to point himself out. He is muscular, as a result of his high levels of testosterone. This gives him the appearance of health and strength. He is then covered by his orange skin. This orange skin reminds us of his ruggedness, a feature that developed due to being exposed to the scorching sun of KANTO, made to withstand such an extreme condition. It also has a psychological effect on the observer. The orange skin reminds us of our deep fears that emerge from our primal subconscious past.
The Charizard's demeanor is one of alphaness. He is dominant, assertive, and can be explosively aggressive. His behaviour strikes fear into the more timid, cowardly pokemon
The summit of expression of his masculinity on his body is his penis. The Charizard penis is largest of all pokemon. As the penis is the penultimate symbol of manhood, this alone would suffice to make the Charizard the most masculine of pokemon. This large penis is able fulfill the desire of the neediest of females, being able to more than fill all the recesses of the vagina. Its length ensures that when it ejaculates, the potent Charizard seed will immediately enter the womb of the female the Charizard impregnates.
In total, the Charizard expresses this masculinity in a most exemplary manner during mating. When he fucks, he unleashes the entirety of his lusts and desires upon his partner without any restraint.
All this is the reason why the Charizard is the epitome of masculinity.