Titan, very very easy. Titans are practically useless in Scourge of the Past for starters. Next yp is the fact the only really viable options are top tree Sunbreaker and all of Sentinel. Striker and the other two Sunbreaker trees are pretty bad. Sure they have One Eyed Mask and Insurmountable Skullfort but that's just about it really. Sure the other exotics are good but they're severely outclassed.