It’s hardly prevalent in Garry’s mod in my experience. In most gamemodes it’s impossible to perform ABH.
In most servers where bunnyhopping is possible, (excluding bunnyhop servers), it’s hardly faster than running normally unless the server was built with bunnyhopping in mind. For servers that don’t try to foster it, the speed gains from bunnyhopping are slim to nonexistent in most cases.
In regards to skill requirement, if you want to be good at bunnyhopping, it takes a good while to master strafing to get a consistent sync rate. ABH is extremely easy and it took me less than a minute to figure it out in single player.
There’s not really much you can argue other than the fact that both ABH and bunnyhopping are both exploits that require a certain degree of skill. Bunnyhopping is difficult to master and ABH isn’t intuitive to use on smaller maps due to the fact you don’t have eyes on the back of your head.