Yeah, the WvW was never balanced when I was playing. There was 1 dominant team that seemed to have a ridiculous number of people, crushing anything they came across with zerg-power. At the end of the last day, they made like 25-50 siege golems and cut through the gates of any forts we had like butter...
However, I was able to organize some our team for a bit to beat back the zerg. The key was to defend a fort using lots of siege equipment, as well as having people down on the ground fighting to act as a buffer to keep the enemy away from the walls. We were able to destroy much larger enemy forces quickly and easily like this. It was a lot of fun crushing a huge army like that so easily, sending the zerg into retreat.
It didn't fail until people went off to do other things and allowed us to be overrun (no buffer of people fighting on the ground). It seems quite easy in many forts for an enemy elementalist to just drop an AoE on the walls, killing the seige equipment operators and destroying the equipment itself. And you can't place arrow carts or ballistas farther back on the wall, since the arrow carts require you to be able to see and click on the ground you want to attack, and the ballista needs a clear field of view. In fact, the ballistas needed to be place right up on the wall's edge to avoid being blocked the lip of the wall (which would leave you unable to shoot anything except very distant targets). So you need to have a decent army of allies fighting on the ground.
I wish there was another day to play because I would have tried to organize some recon so that we could know when the enemy army was coming so that we could get back defend with sufficient numbers. There's limited waypoints to respawn at, so it shouldn't be hard to have some people keep an eye on the routes an enemy army would come from, especially on your home map.
Apparently, money is supposed to get easier to obtain as you level higher, so blueprints may seem cheaper and cheaper. Once money isn't a concern, supply may be the main factor. I only saw a supply camp empty once, and it was while we were rushing to build siege equipment to defend a local fort. But if blueprints become even more affordable, forts may routinely become well defended with equipment that you need more than just a ram to attack, and you may even see equipment being built during pitched field battles.