Well, i disagree.
Imo speed on horseback is important, but so is damage. The difference between one-hitting an enemy and having to hit him twice is insane, as you will rarely be able to hit the same enemy twice from your horse on a big server.
I had 18/18 last gen, and that was nice, but the gys who took 2 hits were a pain in the ass.
This gen, i am going for 21/15 to try something else, then i will decide afterwards what i like the most.
I think i have a different way of playing cav, the fatc that he heirloomed his courser tells me that he spends all the time backstabbing unaware enemies, where he can simply gain insane speed and hit them in the back with a lance that 1-hits because of the insane speed bonus.
Ofc i do that too, but i use a sarranid horse because it is better at cav vs. cav and it is also better against people on foot who know you are there. Imo, it is also more fun to ride :p