If Jagex moved against Runelite even a little bit, the player base would instantly abandon the game. It would be suicide for jagex. They know this and so do the players.

Honestly, the symbiotic relationship between jagex and the players is what has made the game great. Without the players checking jagex, and without jagex ignoring the idiots on reddit who suggest 'improvements' (while listening to the users with nuanced suggestions/critiques) the game would have died a long time ago.