Hello,
in my opinion, the main problem is cav's damages.
Indeed, most of lancers can one-shot almost everybody with a simple hit (in other words, not a couched lance hit), even if they are not at their full speed (and even if you have a heavy armor). Moreover, lancers use very long weapon, so most of inf can't do anything against them. So for me cav, and in particulary lancers, are OP.
Besides, i don't know if it's the same in NA, but in EU, the number of cav increased a lot those last months. So it's not rare to see like a dozen of cav (and 75% of those cav are lancers) in the same team, which is a bit unplayable for inf who don't have any way to protect themselves.
As far as i'm concerned, the only way i found to protect myself against lancers was to become a 1h cav. In this way, i can flee ennemy lancers ><. Of course, i can one shot many poeple (with a mw military cleaver and at full speed i can), but 1h/2h cav take much more risk than lancers, because they are vulnerable against 2h sword, most of polearmes, and 1h sword (if they know how to jump slash or if they know how to use a thrust).
So in my opinion the main problem of cav balance is the fact that lancers do so much damages in compare to other class. And the high number of cav is due to this problem, because we often see lancers with 35/45 kills at the end of a row, so poeple want to do the same and become lancers.
PS: Sorry if i did grammar mistakes, i'm not english so i still have difficulty in writting english correctly ^^
PS2: And please don't say me that lancers do many kills because they are skilled, maybe 10% of them are, the rest just use a (herloomed) sarranid warhorse + (herloomed) heavy lance and one shot everything without taking any risk
PS3: Siiem, you're realy luckie if you're one shot only by lancers who have mw heavy lance xd