Trample feels very bad in its current iteration. Felled trees, ores and berries, all buildings (even Lumber/Mining Camps) will cancel the charge, making it nigh impossible for strategic use. It is hardcoded for use only in open fields, in which case you are lucky that your Cataphract will hit more than one unit for 12 damage.
Remember, this ability locks your unit into place for the duration, is very easy to avoid, has a longer cooldown than regular charges and gets cancelled if you command-move the group when there are other units besides Cataphracts in it.
As a Knight replacement, this is overall just awful. The Cataphract might have more health, but this means nothing to counters that generally overkill these type of units due to the absurd multiplier. Cataphracts, like Elephants, suffer from the exact same design issue of making heavy units juuuust barely worth it for the price, rather than compensate for strength in numbers with some kind of advantage.
Yea, there is the Imperial tech that makes the ability way better. But, I ask you this. What the hell is the point of an ability whose prime function is not available til the game is effectively ending? If the point of the trample is purely the debuff, then it ought to be present from the get-go. Otherwise, make the ability in of itself worth using and let the tech be a bonus (as techs should be).
In conjunction to the gigantic flaw that is making Cataphracts and Varangians heavily compete in gold cost, the Cataphract ends up being giant fodder with no real use. Charge is an amazing ability for raiding, for mobility and to simply deliver damage. Trample on the otherhand cannot be used for raiding due to it being cancelled by all things, its mobility is also hurt by this and the damage is just bad. The idea that Charge deals more damage than a Knight’s autoattack makes it viable as a mechanic. Trample dealing 12 damage literally makes it a worse option than just autoattacking units, and it is quite literally not worth using.
Literally!
There is the idea that you can snipe siege with Cataphracts, but I find this to be niche as it can be done with regular Knights as well, though obviously not to the same degree. The reverse cannot be said however, as Cataphracts are just awful raiders. I really urge that developers take another look at this ability.