The thing with combat is that there's always a chance of you getting a crazy good drop whether it be just killing monsters, or doing barrows. This breaks up the monotony while skills the only thing you have to look forward to is being able to make better or more numerous stuff. Making money with skills, you know exactly how much your gonna make with however amount of time you spend doing it. With combat it's different. My advice would be to buy full guthans and a whip (if you don't have it already) and going to the greaters in karamja caves where the metal dragons are and kill them for clues and repeat. The clues will break up the monotony if you get bored easily. (usually it takes me 40-60 minutes for a clue). You could also do barrows with guthans so you could do that too.