This is all completely fair - I'm just coming from the perspective that Sodhi has already been thrown in the deep end and our alternative in the squad is Bracewell. And also that, while I do like selection based on proven domestic performance the vast majority of the time, I do believe that on occasions it can work to choose someone with good bones and back them for a period of time.
It's horrible selection that both Bracewell and Sodhi are in the squad, neither of them have performed consistently well domestically and in the case of Bracewell, since being dropped from the test eleven, he's hardly set the world on fire in his attempts at making it back in the side, he's not even been the best bowler in CD.
Picking someone with "Good bones" - look, if you're a bowler in the NZ scene and can't get your domestic average near enough to thirty, you don't have the bones for test cricket. The domestic scene is littered with batsmen who average less than 30, you see that whenever someone like Southee gets to play domestic how easy he finds it to take their wickets. Personally Sodhi just has all the makings of an experiment, he doesn't even really deserve his place in the ND side, let alone the NZ one. If you're asking me, Wagner has more makings of "Good bones" than Sodhi.
While I'm not writing off Wagner completely, I have far less faith in him than you and I wouldn't put his overall poor career figures to date down to bad luck. There's some hope there still - while he doesn't have the natural physical attributes of Southee or Boult, that's actually not what's been holding him back - general lack of control, trying too hard and at times perhaps lack of sense being more pertinent. And that horrible seam position - ugh. I'm not holding my breath for a big improvement tbh.
Ideally for me, we'd be playing both tests on a Basin Reserve-like pitch identical to the one vs WI, where you could (just) justify four seamers, and we'd select Wagner as third and Henry/Milne/Bennett/Wheeler as fourth. Most likely Henry as I can most see him replacing Wagner as third seamer. Then reintroduce faith-in-Sodhi for the West Indies tour.
Go review his spells in the West Indies when he first got picked, he consistently beat the bat, troubled the batsman and in many peoples eyes, was our best pace bowler on tour without getting the rewards. Also review his performances against England where he rushed players like Bell, Trott and Pietersen and more often than not was the one to get their wicket. Like I said before, he's trying too hard to bowl quick which means he's scrambling his seam, losing control and trying to play a role that McCullum seems to want him to play. He's also not getting to bowl the long spells that he's used to bowling at domestic, he's a guy who likes to bowl as many as twelve in a spell, he's getting four to six.
His performances at domestic merit him being in the test squad and as I pointed out, statistically he's not performing any worse than most of the players we've tried in their first few seasons, he's also part of a bowling unit that has looked as effective (the three seamers) as anyone has since Bond last played, so I think ultimately, he deserves another couple series. You can see also by the faith shown in him by McCullum and Hesson that they like him in the side.