Yannick, do you think that native areas are inappropriate on certain parkland northern courses or even warm season turf areas?
Personally, I think they are inappropriate to some course designs. My home course here in GB Wis. for instance. It is a lovely parkland course, yet native grass areas just isn't a fit. Our rough areas are rotary deck mowed around not so dense of wooded off FW areas, where the penalty is a jail escape punch out, shaped or whatever, but with a turf of blue grass mowed to a height that most balls can be found readily.
IMHO, Erin Hills may be a course that too much dense native is in deed native prairie, but too much of it. And, I have no good idea how that can be mitigated, given that particular course design, where is is appropriate and native, yet a pace killer and unplayable in many areas.
There just doesn't appear to be a good rule of thumb of where native is good, or overdone, or mis-specified by the archie, IMHO.