not necessarily: What can stop you from building 3lvl warrior to fight against an army led by 2lvl commander and lvl one thief with assasination? This is a very flexible expansion!!!
Yep, thats why I bought it! I was just poking around here looking for variants on using the heroes on a single per game basis, much like Battles of Westeros has Commanders, which I really like! I suppose coming up with a level cap like you suggest, and building however many heroes you want within the cap would be pretty fun. i.e. 3 level 1 heroes, 1 level 1 with 1 level 2, or a single level 3.