I believe that ‘designer’ is just an umbrella term, meaning nothing in itself.
Just like programmer, doctor, engineer, lawyer, and pretty much every other profession dealing with a large, complex body of knowledge and skills, designer is a generic term. It points in a certain general direction, and that’s all.
Landscape Designer is not the same job as Graphic Designer. And I find it difficult to imagine someone would argue with that.
Nobody hires programmers expecting them to be equally good at making firmware in assembly and designing large class frameworks in Scala.
Thinking that design is any different means not understanding the amount of applied cognitive psychology that makes a good interaction designer, or the amount of human factors involved in service design, or, perhaps most ludicrously of all, how specialised one needs to be to really master a useful fraction of the countless technologies used in front end development.
This doesn’t mean that the occasional very experienced designer can’t be well versed in many of these. But most designers won’t, and it is counterproductive to make them think otherwise.
Saying design is all the same risks fostering a culture of amateurism and false expectations. Which does no good to beginners and, in my experience, angers experts. Most importantly, it doesn’t work.