IRL, anything over a D-cup (US sizes) on a thin lady is understood as having pretty niche appeal. In porn games, I'd say anything over an F-cup (US sizes) is considered niche. IRL, a 6" long penis is considered above average, and 7" or above is fairly niche. In porn games, we don't tend to get measurements specifically, but the rule (which definitely doesn't apply IRL, given how few porn starlets fuck literal horses) seems to be that bigger=better, basically until it's reasonable to assume the head of the penis should be visible from a lady's mouth when the impossibly huge-cocked guy in question is having sex with her. At that point, I'd call it niche.
Are porn game standards for what's considered sexy actually pretty weird? Absolutely! But that's what they are, regardles of how you may feel about it.