There is no longer any way to defend his performance this year. His being in the lineup is a result of lack of options. We don't have anyone on the bench that can play 1st base and our next option on the farm is AJ Reed.
Taylor Jones is an interesting prospect:
https://www.baseball-reference.com/register/player.fcgi?id=jones-000tay, but White and Kemp's lack of options are probably preventing both he and Tucker from getting called up. That's frustrating so the popular opinion on here is "cut White", but believe it or not he and Kemp both have value they aren't going to let them go for free unless that's the only choice they have.
We sure could have used JD Davis over the last month and until the break (.270, 8 HR for the Mets), and maybe one of the lottery tickets we got in return (all of them are doing terrible at A level btw) will turn into something, but as it currently stands that transaction is a cautionary tale for not trading guys away just because for the moment you have congestion at a certain position and they are not performing yet.
I do think White has to go one way or the other when the time is right, but especially with the perspective we should all have about how unpredictable prospects performance at the MLB level can be, it's moronic to let him go for nothing when you don't absolutely have to. Which is exactly why Luhnow hasn't yet.