Battle requires less teamwork than siege.
If you kill someone in battle, he stays dead. You just helped your team, no matter where, how and why.
In siege, killing someone has no value in itself, unless it happens at the right time in the right place.
This is also the reason why most pubbers, including me, don't play siege often - the amount of teamwork needed for the game to be REALLY funny and challenging is more or less impossible to achieve. That's why battle is better suited for pubbers.
Siege takes too much teamwork for a pub. So much that winning generally comes from a map being unbalanced, not because one team played slightly better than the other, or in the case of defenders, they could dominate for the first 5 minutes then get some unlucky deaths on their team and lose the entire round. Especially when there are few players on, one untimely death for a couple defenders is enough to lose the round, regardless of how long they were alive or how many people they killed, which is terrible considering how balance is done. Often times it seems like there are 2 highly skilled players carrying 10 gen 1s while the other team has 20+ average players, where the two highly skilled players make up 50% of their teams kills, so if they both die at the same time, it means their team loses(I can't recall how many times this has happened to me, it's probably the biggest reason as to why I don't play siege).
Unless it's the middle of the night, your clan won't be able to really utilize their teamwork due to there being too many players on the server and banner balance taking a back seat to other types of balance. Ladders can screw up game balance so much that regardless of what the defenders do, they'll never be able to hold the walls. Trying to break down 5 ladders going up all at once at separate areas of the castle while defending the gate and the siege tower when your team is comprised of 80% pubbies 10% your clan and 10% another clan, is frustrating and nigh impossible. It would be completely different if it consisted of 80% clans and only 20% randoms, but that -never- happens.
Respawns are another problem with siege. You're supposed to be utilizing teamwork but respawns themselves only serve to break-up teamwork. For defenders, you spawn in random locations, so even if you're trying to stick with your clan, you have to deal with being dead for 30 seconds and the time it takes to run back to where they were when you died(assuming they haven't moved from that location in the 45 seconds to a minute that it took you to get back). For attackers, if you die and the rest of your group doesn't, you're alone for the next 30 seconds or so, unless the rest of your clan dies as well.
Most games now-a-days have adopted either a wave respawn or the ability to respawn near your squad/brigade leader because they've realized the limitations on teamwork due to respawn mechanics. Battle doesn't have this problem because there is no respawning during the round.
