I'm happy for this lens. I personally don't need it, because I purchased a 16-35/4, but if I didn't already own one, I'd definitely consider this, because:
1. I almost never shoot below 24mm anyways, because I don't do landscapes, my animal subjects are too small, and there are few stills that I shoot where I need me to go that wide. Number of landscapes, lakes, sunsets I shoot in an average year = 0.
2. For the longest time, I simply used a 10-18 on a 80D for the same task. In fact, the only reason that I purchased a 16-35 was because the price was good, and to have access to that wider focal length without packing an 80D on a trip.
3. For the incredibly rare times that I want to shoot that wide (a sunset on a hotel balcony, for example), and I want a good exposure (as opposed to just snapping something from my smartphone to record a memory), a STM lens that's sub-$500 would be wonderful. Plus, it is probably going to be half the size of the L.
This falls into the same reason to build a 24-105 STM or EF 70-300 (nano) or 100/2.8 macro (non-L) -- some people just shoot these FL's so rarely that they have a hard time justifying $1000 lenses in the "tier 2" L collection (like f4 L zooms). Because most photography is just a hobby for me, I buy the best I can afford for the stuff I really like shooting, which ends up being macro and wildlife, midrange for the stuff I photograph occasionally, and, where there's a low cost solution, "something" for the things I shoot rarely.