Im 100% on board with replacing a class with the Darkhan as a fun and thematic Heavy Infantry. It doesn't need to be a top tier heavy inf like the Oathsworn or the Varyag to immensely help the faction. A Darkhan on top of giving the cav equivalent lances and horses to other heavy cav and making Spear Infantry a proper medium infantry with 80 speed would be enough to help the faction.
Not to resurrect some forum DLC content, but for funsies I hopped on an East Asian servers and tested the waters. I made 2 discoveries.
1: 250 ping is unplayable
2: It didnt matter.
This makes me happy because it was your only argument I couldn't immediately disprove with actual stats or anything.