My question too... why is it that our boys in particular batters taking so long to settle down in international cricket? Sure you don't expect and don't want huge highs at the start then fall over but you would expect guys that have played 20-30 games would have settled down by now. I think Henry Nicholls is the only bloke to nail his spot in recent memory. Rest are there and there abouts. NZ domestic cricket quality is definitely one of the top 3 in the world along side Australia and South Africa. We have less teams, to make to domestic cricket is not all that easy so these guys should be seasoned and should take to international cricket like fish to water. Sure our spin bowling stock in domestic cricket is not all that great but I believe we have one of the best fast bowling domestic cricket set up in the world. Munro has played nearly 50 one day games at an average of 25, G Phillips averaging 15 @ SR of 100 in T20s, Tom Bruce averaging 18 @ SR of 128 (which isn't bad), Geroge worker 34 @ 71 SR (That's not bad too), CDG in one day averaging 30 @ SR 78 (surprised as I thought he smashes it) and 14 in T20s @ SR 139
Granted they haven't played lot of cricket yet but they are not young either barring Glen Phillips. Most are over 20 and almost nearing 30. You'd expect them to be consistent given their experience. Somewhere along the line we are producing a lot of batters that are just there and there abouts. If we can find a batter that can average 40+ in One day and test cricket we will be in a much better place. I'm not sure where we are going to get that from in the very near future.
"NZ domestic cricket quality is definitely one of the top 3 in the world along side Australia and South Africa" - even assuming this is true (I'm not so sure), exposure to different conditions, kinds of opposition, pressure situations etc would all surely play a part in making international cricket a big step up.
" I think Henry Nicholls is the only bloke to nail his spot in recent memory." - When it comes to the batting, one offshoot of selectorial consistency is that over the last 4-5 years the batting has continued to revolve around a core of Williamson, Taylor, Latham and Guptill across formats with Raval more recently taking over Guptill's spot in tests. There have simply been no vacancies, Nicholls has taken over McCullum's spot and that's it. Sure some of the batsmen haven't come on as we would have hoped, but there hasn't been much room or promise of selection either.
About the specific players you mentioned:
Munro - Given that he seems to have cracked T20 cricket, his underperforming in ODIs seems to be a mental thing. Then again this is the very first time he is getting a consistent run in the side, so have to wait and see
Phillips - Too early a stage in his development to expect him to succeed in internationals IMO, seems like a great talent
Bruce - Don't think he is international quality, him averaging 40 plus in FC is a bit of an indictment of the domestic scene
Worker - Again decent player but not quite good enough for internationals, don't think there is any expectation mismatch in what NZ are getting out of him
CdG - Like Munro, issues seem mental more than anything else but worth noting that NZ have got more out of him in 2 years than they have from Anderson and Neesham
As to why the newer players are not taking to international cricket like fish to water, my theory is that they are mostly learning on the job (ie. at international level) and NZ are in a phase where they are being offered very little cricket (the current UAE tour is the first full overseas tour in 2 years for God's sake). From the previous cycle, guys like Williamson, Latham and Watling benefited from a rare boom in test cricket for NZ from 2012-2015 where they were playing tests on a regular basis both home and away (around 40 tests in this period, which is a lot by NZ standards). From the start of 2016, to the end of 2018 they will have played around 25 tests, mostly at home, which is a fairly significant reduction in international opportunities.