courser is good for lancing indeed, but lancing does need alot of maneuverability as you have only a limited angle in wich you can use your lance (especially when you couch), offcourse when you are going up someones back that doesnt see you coming you dont have to be able to adapt to his movement (he will keep walking in a straight line). but if
*charging enemy cav frontally
*charging an aware inf man
*fighting at low speed (circling around the inf guy, away from his weapon but ready to ride in on him when you see an opportunity)
in these cases that agi can be pretty nice, even while being lancer. you might have to dodge a swing/stab while stabbing the enemy at the same time.
note that im not cav anymore and was never good at it, but the better cav players always suggested me to go high agi.
if you want a real hybrid you could try the full six hybrid
Level 30
Strength: 18
Agility: 18
Hit points: 63
Skills to attributes: 2
Ironflesh: 5
Power Strike: 6
Athletics: 6
Riding: 6
Weapon Master: 6
Polearm: 156
but i think you could get a char with 12 str, max if, about 6 shield skill, 4 ath and get a pretty nice hybrid too. (1h on foot, lance on horse)
i would say try it out and see what you like the most