Fixed for you. Siege valor isn't that hard to get, unfortunately the easiest way to get it is to totally ignore the flag and run around on the walls killing archers/etc. So if you actually want to try to capture/defend the flag, then yes, valor is hard to get.
Arguably, valor is quite difficult to get as an attacker. Defense almost always has a higher average score, and since valor is calculated for the entire server, attackers are at a disadvantage. Of course there is also the option to try and help your team by ninja-ing the flag, in which case you will most likely (assuming you are a good ninja) meet very little resistance, and therefore receive little score. Like camping the flag on defense, it is the more helpful strategy to your team (debatable, perhaps, but usually it is nice to try and ninja at least once per round) but less likely to give you any significant amount of points. Valor can be easy on defense if you play the map right. Block a significant chokepoint, and the enemy has to come to you. Cut them all down, and they keep coming back. Of course no one man can hold off an entire army, so this is where someone needs to give up trying for valor and hang back at the flag, or cover other chokepoints. If everyone on defense rushes to the main gate or path of entry, then that leaves you very open to ninjas... it's a risk-reward scenario, unfortunately. Would be nice if you got rewarded for playing smart, but I frankly don't see how that can be possible.
Rewarding points for standing near the flag just promotes leeching whilst sitting next to the flag, and frankly you want to try and slow down the attackers by fighting them on the walls as much as possible. If it is a constant fight on the flag, with attackers meeting no resistance up until that point, defense might eventually get overrun, depending on the map's spawns. Ideally attackers would get points for the amount of time they spend in the flag's proximity... so even if there are several defenders on the flag, and it isn't being capped, that man can still get rewarded for his efforts. On the defensive side of things, perhaps any score you would receive from combat gets multiplied if you are within the flag proximity, so you have to be a part of the action at the flag to get rewarded. But once again, in my opinion it would be nice if we could encourage defenders to fight on the walls to hold off the attackers as long as possible, and then fall back to the flag only when the time is right. That would be the tricky part with rewarding the smart players on defense.