It is possible to have too many rules...
I like Dragon Warriors' simplicity - there are no rules for things like cover, running through combat, charging, weapon reach, etc., and putting them in (and everything else that comes with it) would just create a bulky system like D&D or GURPS.
If your adventuring party wants to hunch behind their shields and charge a sorcerer, hoping the shield will bear the brunt of the next
Dragonbreath or
Shadowbolt that comes hurtling their way, then give them a bonus to their Evasion and say their shield is destroyed by the spell, should they succeed their Evasion roll.
In a role-playing game, where almost
anything is possible, rule systems that attempt to cater for all of those eventualities just end up bulky, expensive and, ultimately, less fun to play - you're either at the mercy of the rules lawyer, or you spend too much time flipping through supplements to find the appropriate rule.
Note that the Dragon Warriors rules are pretty combat-heavy already, and the rules set the tone for the game that you play. Too much emphasis on combat and you'll end up with a D&D murder-hobo hack-and-slash adventure, losing the elegance of DW in the process. In combat, the narrative is much more your friend than the rules - if you can keep the players in character, even when they're rolling the dice, then you're doing your job as the GM
.