You unfortunately misunderstood me because you didn’t take my full sentence. The correct quote should include “In castle age”. 
In Castle Age, Mongols have the most options in the stable with Tatars and Cumans (“co-richest”). “Better than Persians”, because Mongols have got FU knights and camels, besides the strongest Steppe Lancer in the game and even the strongest light cav. (except in melee after the Bulgarian’s castle unique tech, hard to get before at least mid-castle age). And that, for a civ. not even labelled “cavalry civilization”, like for instance the Persians.
And that’s all without even considering heresy -which the Persians lack-! It last saved Viper in one mind-blowing AoElympics game (see https://youtu.be/xW8SqnmmL4g?t=1731, [reads twitch chat: “thank god Mongols got heresy, huh?”, on which he answers:] “Yea, without heresy, [I] would have been super-dead.”).