this would make polearms the premier option for cavalier. That's not good.
Fair point. Having your mount disengage for a lance strike before moving in close to disrupt an enemy makes sense thematically too.
It's allowed by 5e. It shouldn't be. There isn't really an easy way to make this clear however.
It is not allowed in base 5e- since there is no fighting stance or style that allows a Player Character to dual-wield non-light weaponry.
Student of war and rallying cry fit the theme are are competitive with other 3rd level features.
Know your enemy is a trash feature imo. Please suggest a replacement.
Inspiring leader and bulwark are both good. It's missing an 18th level feature though.
To replace Know your enemy my friends had a few suggestions. I think our best idea is an ability that gives critical damage to the next attack (from an ally) after the warlord spends an action revealing a 'weakness'. Vulnerability is also applicable- but maybe too strong? Limits for this feature: using the feature a number of times for an Intellect recovering on a long rest, the next ally in initative must hit their first attack, or tie in 'Know Your Enemy' requiring observation of an enemy before using this feature on them. Hope these ideas help.
What fighter archetype is missing?
Reviewing the core book, I had not realized how much homebrew I've used for the Fighter class. Battlemaster was spread across the entire class for manuvers (love them), Eldritch Knight & Arcane Archer is the Magus class. Scout was put into Rogue. The only one I can really find is Champion and Brute- which aren't interesting options anyway.