Many players who cry "OP" seem to forget two things: (1) some builds have a natural advantage over other builds and (2) not everything is always balanced in a game with level-based character development. Of course a long polearm can easily destroy a charging horseman, and a 2h can beat an equal opponent with a smaller weapon, but it's also quite straightforward to say that the more esoteric builds can appear OP simply because they are such an unfamiliar foe. HA are a good example of this because of their demanding stat requirements and the generally great skill required of those who use this build. What separates a HA from a regular archer? They can charge infantry, but so can other horses. They're also faster, sure, but so are many lightly armoured archers. These are simply two advantages which become terrifying when used properly but are otherwise fragile when use in the wrong context; a HA that charges into spears will fall to pieces against a moderately skilled opponent, just as a HA will die when trying to engage a competent 2h in hand-to-hand combat. There's no foul in playing to your strengths and exploiting inexperience.
The other oft forgotten feature of cRPG is that characters develop positively. Moving from a light bow to a stronger bow doesn't mean that both bows must be somehow equal "in their proper contexts." It's reasonable to say that some gear is objectively superior to other gear by most relevant standards. I'm comfortable with the idea that club-wielding peasant, no matter who controls them, will never take down a conscious Lady Gaga on her Apocalypse Horse. Skilled players worked to get what they have and to disagree with an this incentive-based system is to reject cRPG altogether.