You may be right about this, z... but... you may equally be wrong.
If what he's done in the past couple of weeks is reflective of adjustment to the majors, that might suggest that keeping him in the platoon role would be quite adequate. Yes, his overall numbers are still bad... but that's inevitable, given his early performance. Whether the improvement is real, or a mirage, is something that we cannot honestly evaluate at this point; it's too soon to know.
So, do we throw in the experiment, send him back to AAA, and... do what, instead?
As an aside, I'm gratified that the earlier "he's not good enough; find somebody else" about Justin Crawford have pretty much died down. This is a similar situation; bad start, followed by improvement. Overall, he's a 0.0 WAR player at this point (B-R); but the last month? Rather better than that.
Rookies. If you want to bring rookies into the major-league lineup, you're going to have this kind of thing. If you aren't willing to put up with these growing pains, then you better get used to huge payrolls filled with declining older players, who never quite measure up to the expectations you had when they were signed to long-term, expensive contracts.