OP, your image of KILLZONE is only showing the "recommended" warzones, you have to search for all active warzones to see them all. You can also use the website. This would give a more accurate comparison. Although usually only 3 or 4 have decent numbers so I doubt it would make too much difference.
Personally I find the mp in shadow fall very dull, the gunplay is just weak. No recoil or impact, just not satisfying to shoot people. They tried to chase the cod audience and failed. The maps are also average at best. Kz2 was brilliant, incredible gunplay, awesome maps but it didn't take off like they wanted so they made it play more like cod and killed their fan base instead of just building and perfecting their own style.
It may sound silly but the sp being so bad also put me off playing the multiplayer or spending any more time with the game. They've completely killed the franchise for me so I'm glad they're making a new ip. It needs to be very special though to get me to even look twice.