What advanced features did you expect to work? When did you buy the router with these expectations? Asus doesn't pay any of us here either, but we find ways to make the hardware we purchased and supplied firmware work as well as it can. Yes, this is a moving target. But so is anyone else's products in the consumer space. And the competitors fall far short of Asus' efforts, IMO.
Security updates are not just to protect you, per se. But to also protect the equipment too (including all the devices on your network) from being put to use in a larger attack as part of a botnet network that does more harm than spying or collecting your google history.
Your priorities should always be security first. Browsing history hijacking is 1990's. I'm sure there are more important digital assets that would make you a valuable target. Even if those assets are just your devices put to more nefarious purposes.