Im just gonna leave this here, since I really like the strategys this game mode offers in itself.
Since this is the PvP-Mode we are talking about its already clear, that this map should be designed more around actually fighting other Players, so:
What if the format of Stronghold would be changed to something like 7v7 or 8v8?
Moreover Doorguard-NPCs should get removed completly. This would offer the opportunity to send out actual players to defend doors. That way, it would be more important sending out a few attackers to face those defenders. Now, if Arenanet would increase the damage Archers do to players, you can create actual threads by mixing up attacker teams with Doorbreakers, Archers and a few players. You also get way more PvP and a use for Archers with this solution
The problems I see with this though is the increased amount of supplys on each team, which could offer the opportunity for a deadly 7 or 8 man push from the beginning. This could maybe addressed by removing the 2 supplys every players gets when the game starts.
At least this seems a better choice then just buffing the Guard NPCs in terms of damage and defense, since this would increase the PvE-Aspect of this gamemode way too much.
Imo, there are more results by taking this step. You would actually create roles and make a diversity of builds neccessary, like tanky/high mobility builds for supply runs, damage focused builds for attacking/defending or even healing/cc focused builds to defend your attack squad.