I recall Canon once stated about another lens, "has a silver ring for a luxury touch."
Maybe Canon should make a Blue Ring or double silver ring for their STM lenses. That would be cool.
IMO, STM lenses at the moment are too under-rated. It's my experience on the M that STM performs better than USM, but that could just be the M.
Canon's consumer kit lenses have been crap for the longest time, but I gotta say...I must admit that their newest line of entry-level STM lenses (after spending some time with them) is actually quite good. Are they "L" quality? No. But they are FAR better than the old lenses, and are actually usable now as a lightweight travel/alternative choice when one doesn't wish to risk more expensive equipment.
I've tried out the 55-250 STM and can compare it to my experience with the 70-300L (on a 7D). Sharpness seems similar(!), maybe with the 70-300 having the edge at wide-open telephoto...the biggest difference seems to be in color rendition. The 55-250 images do lack a certain punch (dull) and need more work in post...I also find the STM focus system to be slower than USM, which factors into servo performance, although the STM did just fine for the concerts I shot...wouldn't recommend for professional use or situations where IQ is critical...but it more than holds its own and when you look at price/performance ratio, it's hard to beat. My point is that Canon's newer STMs are CONSIDERABLY better than the junk they're replacing.
I'll be interested in taking a look at this new 10-18. Seems like the biggest issue is getting good corner performance so hopefully it delivers.