Escaping from lancers is never a problem for me, actually. Both the steppe horse and the arabian warhorse have good maneuverability, allowing you to dodge incoming lancers and even bodyblock their horse, stopping them and getting one or two swings in. All you really need to do is cut them off and block their fist blow.
making 1 mistake lethal.
Well the hitpoint difference between 21/15 (56 HP), 18/18 (53 HP) and 15/21 (50 HP) is quite minimal, because 1h cav doesn't have any points to spare for ironflesh (unless you drop shield or go low athletics, which i would never do).
My favorite 1h cav build has always been 18/18.
For me it all comes down to powerstrike vs athletics. 21/15 has 7 powerstrike but only 5 athletics, making you too slow to chase archers and kinda sucks when facing multiple opponents. However, the 7 powerstrike is nice and makes most swords viable, even against the heavier armoured guys.
18 / 18 hits the sweet spot: power strike 6 is 'just good enough' to make swords a viable weapon, but has athletics 6, which is faster than most infantry and 'just enough' to at least be able to harass most archers.
I've tried 15/21 only once and didn't like it because, on foot, having only 5 powerstrike isn't enough to reliably hit heavier armoured guys. Too many glances. But the athletics 7 is sweet.
Anyways, enough of my offtopic rant on builds. Keep retiring and keep making new alts, it's fun and also it's really nice to have several different characters to pick from.