I got one of my long-term Runescape friends into TTRPGs recently so recommended him this, it's still a good read!
Combat in Runescape is a very mixed bag, you write about the Prayer skill nullifying most combat encounters, and outside of PvP where combat really shines, combat in Runescape is overall quite uninteresting.
What I really like though is that a lot of Slayer monsters (and some quest monsters) can only be harmed or killed while using specific equipment. Count Draynor in Vampyre Slayer cannot be killed unless you have a hammer and stake, even if you're max level. Aberrant Spectres really stink, so unless you have nose pegs you're really gonna suffer!
This can be easily applied to TTRPGs, and can make for some more interesting bosses or combat encounters. Either have an enemy weak against a specific weapon, or give them attacks/abilities that can only be defended against with unique equipment. It's especially good if the party face the enemy without the specific equipment first, get their asses kicked, complete an adventure to get the necessary equipment, and then come back better prepared.
Of course Runescape didn't invent this, it's existed in games and folk stories for centuries (Beowulf requiring a shield of solid iron to defend against a dragon's breath comes to mind), but is still something that can really elevate things in a TTRPG.