I'm your level, and I do slayer all the time . . . Probably what you're noticing is the slower experience phenomenon - it is far faster to gain levels in attack, strength, and defense than in slayer. Many people who started slayer after already being a fairly high combat level have zoomed up in combat levels, while their slayer level grew only slowly. Now they're high levels, as you're noticing, but they need to fight these lower monsters to increase their slayer. Also, one way to accumulate slayer points more quickly is to use a lower levelled master for most of the tasks, then switch to a higher levelled one for the tasks on which you receive bonus points. These high levels may be doing this, "farming" for slayer points. Also, slayer monsters do have good drops, and a high level can go through them pretty fast to get those drops quickly.