personally i believe one of two things, 1.YOU SUCK, or 2. You dont know how to flank!
the YOU SUCK one is pretty self explainatory, but the other isn't, you say the possitions are to well defended, well i say they are not, let me lay down some examples, Ragnarok, If the enemy team has control of the hill they normally are ignoring there own base, so you have to be a sneaky, and get to their base, once there you can start taking vehicles and weapons, then shooting them in the back. the square maps such has haven, adrift, and abandon, all are very easily flipped, Abandon for example the main structure is the main area to post up in, if you use jetpack with stick grenades they will run away in fear, heres what you do, fly up stick a guy, drop down, take ramp, kill guy, jetpack up again kill guy, and there you go top is yours. those are just a few examples,
P.S. If you have ever played Gears you might know this stratagey, but when an enemy sees you, and you see them, (PV) you can juke them out, you act like your about to rush them then stop and fall back making them come out of where they are hiding to kill you, but then since you enticiapated them, you can blast/grenade/or melee them with ease,
P.S.S. Stop looking for things that are good and bad and different from the previous games, ( Power weapon control, spawn control, map control) and look for new ways to deal with the new game, you might actually like them