@Espadas Any game with more action-oriented gameplay where you can dodge attacks with skill you can generally solo any content with enough time and skill (and recovery items!).
Most raid bosses are set up to fight raids so a lot of the difficulty in fighting them is based on their abilities that target players other than the tank. Summoning allies, wide aoes, CC'ing the tank to attack others, attacking people at random, otherwise forcing players to pay attention and move around and such. If you have a character that can avoid most single-target attacks reliably and the ability to use healing items to recover after the unavoidable ones, and ways to avoid/remove various gimmicks like debuffs, dots, terrain effects, then you can basically solo anything? Would just require the ability to focus and not mess up
at all over the course of a few hours, and knowledge of the boss's patterns.
Games like WoW and what I played before it, EverQuest, made that impossible because they remove most player skill from the game so you can do 99.9% of the content without doing anything more than pressing your macros in the right order, but you need a tank and healer (and maybe CC) for some content because group/raid enemies have big numbers. Not that it's a bad thing necessarily, just a different style of game.