Comp and max cape don’t have the same stats. There is a difference in combat strength, defence, lifepoint and prayer. Comp cape also requires completion of all quests, diaries, and other arbitrary requirements like livid farm. It’s better stats are justified. However, killing bosses a single time does not offer any benefit to a player at the end of the day. You don’t complete anything by having one kill, apart from some weird title, whereas other titles are not required.