I'm not entirely sure what to tell you here. Yes, the game was designed as a multiplayer online game, so teamwork is encouraged and inteded. You CN be effective as a solo player, but never as much as many players collaborating.
If you find yourself outside of your power range with the Forgotten you are overextending your forces. Your progress will be slower as a solo player, because you will not have the same benefits an alliance has with multiple POIs. So make sure to stay at an level area equal to your own defense level to avoid the problems mentioned above.
