

The idea is that you want to guarantee that your commanders only have strong tactical options for each battle phase, and eliminate the chance that they'll pick a crappy tactic because they had a small number of heavy infantry or something mixed in. The only exceptions as I recall are some of the special faction units like Cataphracts, who have a strong skirmish phase (horse archers) and strong melee phase (charge/crushing charge), as well as Scottish pure pikes (schiltron formation) and English Longbows (mostly archers with some pike units mixed in). I might be wrong, but that's what I remember reading and it's seemed true in my experience. The reason for this I guess is that an archer/pike combo gets strong performance at both stages of combat, both skirmish and melee (particularly with a commander from a pike-friendly culture), whereas a pure heavy infantry army can get torn up in the skirmish phase. Even an anglo-saxon nation would be better off building a pure mix of pikes/archers than with their nation-specific housecarls (with heavy infantry and commander bonuses). I may be wrong, but from a min/maxing standpoint I think it was most effective to build pike retinues. I think 'generic retinues' mean the non-faction ones, so Cataphract/Housecarl/Longbows etc are out.
