I don't know that I would: The dark malt is a part of the flavor profile of the beer. It is easy to add too much and run over into astringency but in a small amount, you need that kind of burnt flavor. Remember, a mild doesn't have a lot of other flavors going into it. To reduce the astringency and bitterness, cap the mash before sparging with the dark grains, that limits their contact time and extraction.

 

That might be so in the home brewing community, especially in the US and according to BJCP guidelines. There are a few real world examples of breweries fitting the guidelines, but not many and they seem to be clustered around Manchester / Leeds area. The vast majority had no roast malts at all or very little. In my experience the mild ales I've drunk over the last forty years have had no roast flavours to speak of.

Here are a few typical examples...

http://barclayperkins.blogspot.com/2017/01/lets-brew-wednesday-1960-whitbread-best.html
http://barclayperkins.blogspot.com/2017/05/lets-brew-wednesday-1963-lees-mild.html
http://barclayperkins.blogspot.com/2018/05/lets-brew-wednesday-1958-william_23.html
http://barclayperkins.blogspot.com/2018/05/lets-brew-wednesday-1959-adnams-xxx.html

this one with some roast barley...
http://barclayperkins.blogspot.com/2016/12/lets-brew-1969-truman-lm.html
and this one with a smidgin of chocolate...
http://barclayperkins.blogspot.com/2012/05/lets-brew-wednesday-1987-boddingtons_23.html