Perhaps the idea of fielding lowly 'scum' is to try to force the nasty knights into attacking where (and what) perhaps they don't want to...
But of course, altering the game to give you the gameplay you want is fine. It's an easy set to tweak after all. We enjoy it at my club and have been playing a few 'Dark Ages Arthurian' games with it as well as straight Fantasy.
I like some of the house rules in the document and may give some of them a go. We have found wizardlings not too powerful in our Fantasy games, but we usually field light foot as 'wizardlings' as they aren't too powerful and can either cast a spell or move/fight, etc, so it's not too unbalanced...