In terms of boosters and other special effects that's what's at the heart of prayer. It's a way to give players advantages and benefits in combat which other MMOs usually offer players by trading skills, like making armor runes to add to your armor or RuneScape gold enchanting your weapon to be more powerful or other.

RuneScape does not have that, therefore, it requires prayers to function like that and provide players with the sort of option they'll need as content at the end of the game is getting harder and harder (God Wars, Dungeoneering and other bosses are great examples) alongside gear which will only offer so much to players, and this is the reason why potions are becoming stronger too. In reality, gears and supplies (as as well as prayers) were getting too powerful in terms of PvP, hence the absorb effects on armor.

My point is, RuneScape needs an aura slot to efficiently improve the game. It's hard to comprehend for those who hasn't gotten a 99 skill or isn't getting a good enough combat level to take on difficult bosses where it's not possible to just hit Protect from Range/Melee/Magic and everything is fine however it's one of those things that the game must have to be able to deliver an ever-growing amount of challenging content in the future.

The benefit of assigning it to a slot in a statslot is that JaGEx will then be able to allow, for instance, usage of Aura slots within the Wilderness (as an instance) which balances Boss-killing (and other high-combat PvE content) and PvP.

Instead of complaining about taking a feature from other excellent MMOs feature, maybe you'd be better off thinking about the reasons it's coming out and what the game is aimed at rather than just complaining about it. what's the problem is that the majority players nowadays doesn't have the experience behind them to percieve the implications of cheap OSRS gold.