No, the difference is explained in post #7.
Newer routers may change the channel multiple times a day, including Asus models.
That explanation doesn't really make any sense to me, basically saying 20/40/80 won't pick 80 if there aren't enough sequential channels, but then it gives you the option to hardcode to 80 which is an impossible width? Why would they even give you the option to hardcode to something that is going to work like crap, unless there was some other intention (such as preventing lower speed clients from connecting). Though I guess a lot of things in the Asus GUI don't make total sense so wouldn't necessarily be surprising either.
On AC I've only seen the option for periodic rescan start to pop up more recently in newer firmware, and I've never seen it enabled by default. On AX it is common though, at least in the the limited number I've worked with so far.
But if you don't have control over every AP (which you won't unless you're in a very rural setting), that "constant battle" is probably still better than hardcoding, at least on 5ghz. On 2.4 I do hardcode at home, and periodically do a site survey and see if I need to adjust. But as I rely less and less on 2.4 I've mostly just left it alone lately, one AP is on 1 and the other on 11. AC and AX are quite good at choosing the best base and extension channels in my experience. Your phone is constantly adjusting its cell parameters to get the best signal, why is it bad if your router or wifi device are? Granted cell towers and even cellular chipsets are far more complex and expensive than wifi, but the concept is still the same. Though a static channel selection should not cause any compatibility issues, unless you select a DFS channel and for some reason a client doesn't support those (i.e. it has a different country code in it).