Mentor rouletting into the level 15 guildhest, B2 is very useful there. Also if I get thrown into Sastasha, Copperbell, or Tam-Tara or any other sub-freeze dungeon and the tank pulls at least 4 mobs to make it worth casting over a blizzard 1. It's not that uncommon for it to be a DPS gain, it's just also awkward and annoying to use.
And I still keep Scathe on my hotbar because it's useful for ARR content where it was designed to be an at-will fire 1 replace, well before the devs keep forgetting to upgrade it for the modern rotation.
Going back to your own point, if the class has that many redundant and useless skills, then there's no reason to even need to increase it over 24 to begin with. Or, better yet, the devs should just lock what abilities could go in what slot so that you're forced to use different styles of skills, such as 3 defensive skills, 12 DPS skills, 5 healing skills, or some other arbitrary delineation and subtype. Going above 24 serves no direct purpose, and arbitrarily saying "Just don't use more if they add more," is really, really bad advice.