I think part of the appeal of Dragon Rampant is that it was designed from the outset as a “toolbox” system that allows quite a bit of room for fitting figures to unit profiles. It is even flexible about unit numbers - units have either 6 or 12 strength points, but what that means in figure numbers is determined by the players. Could be 1 figure per strength point (which makes decent looking units on the tabletop and means no bookkeeping is needed), or units could have few (or even a single figure) with multiple strength points each.
One difference compared to Oathmark is that Dragon Rampant does not require that figures be formed up in ranks, and flanks usually don’t matter for combat resolution. DR is a skirmish, so turning to face enemies is assumed to happen. DR does require that all figures in a unit stay within 3” of one figure (usually the guy closest to the centre).
Another difference, which rubs many players the wrong way (including me) is that the player’s turn ends when an activation roll is failed (the player turn is to activate one unit at a time, until a failure happens or all units have activated). The unit profiles have different activation target numbers for each type of activity, so a player can play the odds a bit by activating units with better odds first, but it is still quite “swingy”. A run of bad luck can make a game a disaster, through no fault of the player. In later games based on the core system, the activation system is a bit less draconian.