Don't be mistaken for thinking that the issue is the 'sacred cow' of respecting source material. Because it's not.
It's that Hollywood roles are dominated by slots for white people (usually men) such that blacks, asians, gays and women are usually left with 1-dimensional supporting roles at best. These 'roles of asian origin' which are recently making headlines are really just a line in the sand where Hollywood unequal treatment is highlighted - Asians can't even get roles that were written with them in mind.
Basically, every role is a white role by default. Most source material is white. Most movies are white. But much of the audience isn't white (not to the extent that the leading roles are). Skrein is, as they say, 'Woke' and understands this and understands that it's not about 'diversity', it's about representation.