The most OP ERK was the one from the first version of the WC. In that version, if I remember correctly, the skirmishers had no bonus against the ERK. In TAD the skimishers already had the X2 bonus against ERK.
ERK are entirely different from any other dragoon too, and the aztec army has many shortcomings.
In the next patch the ERK will receive significant changes. One developer already said that they would be monitoring the performance of the ERK and that other Aztec units could also present adjustments later.
In my opinion, the issue of the ERK has already been dealt with enough. Now we have to wait and see what changes are implemented and how the Aztecs work with said changes in supremacy and treaty. Due to the peculiarities of the Aztec civilization I am almost sure that there will be dissatisfied people after the patch. so, here we will be discussing if the ERK is still OP or if they exaggerated by weakening it.