If you prefer, you can use them on other combat skills. However I am already 50m in Attack, Str, Hp. Scurrius itself was really good Def xp. Also there are lots of alternatives for afk training other combat skills, including mage and range. Like the crabs in fossil island. I was getting like 1m xp (attack/str/Def) per TOA run too, so was getting a 90+ level every TOA run. In my opinion, using them on prayer is definitely a good option in leagues. All the best!