And they did that lense without fluorite element and all special glass and handpolishing ,just with cheapest possible methods.The EF-S 55-250mm STM is one of Canon's gems. The lens scores well in measurements on various sites. On opticallimits and TDP, the 55-250 at 200mm has about the same IQ in the centre as the 70-200mm L IS. I use it with an adapter on the M5. In fact, my copy was sharper than my 70-200mm L IS, and I sold the L lens.
If they would make long lens with L quality to crop sensor it would be better than any big white on image quality. just saying i know they wont make