Kryten: Amazing job on these units. I should have complimented you earlier, but for the first few days all I could say was, 'Gah . . . guh . . . gahga' and drool. You knocked me back all the way to infancy.
Anyway, I think the Chin spearmen make a great back row for the Samurai (maybe 'cuz I'm no expert on the medieval Orient), but I'd really rather see guys with polearms or spears behind the knights. A baronial feudal levy, made up of serfs, wouldn't have had swords, which were very expensive and not much use on the farm. These guys would be more appropriate for, as you say, Franks/Saxons/Vikings/Goths/whatever, tribal warbands made up of freemen.
On t'other hand, I haven't seen any other units that would be better behind the knights, except maybe the crossbowmen (or pikemen, I suppose, but that's getting a bit later). It's not like I'll refuse to use them, anyway!