Most of those guys had a history of performance either at youth or domestic level before being selected though. I agree that a lot of them should never have even been tried as front line spinners but Australia panicked because they were used to winning games on the back of their spinner. NZ haven't had a match winning spinner since about 2004 when Vettori's back issues meant he lost his dip and spin.
Beau Casson - one decent FC season and a forced selection when MacGill retired mid-tour. With touring experience and a couple more years, might have been ok - but was never going to happen with his health issues.
Dan Cullen - one decent FC season, picked alongside Warne and MacGill, actually an utterly crap bowler who should never have gone near Test selection.
Michael Beer - No history of performance whatsoever, other than a column from Warne backing him.
Xavier Doherty - Played U/19s and was a Tasmanian journeyman, but anyone with eyes could tell he wasn't an FC/Test bowler's arsehole. KP can play left arm spin when it's dart-y pies.
Ashton Agar - Missed the U/19 World Cup with injury (with Ashton Turner filling the lead spinner role), but had a good FC record for a 19-year-old just starting. Should never have displaced Lyon, he had no record to speak of.
Steve Smith - Akin to picking Kane Williamson at 8. Always was a batsman who bowled (and could develop into a genuine all-rounder), not the other way around.
Glenn Maxwell - Never played as a lead spinner (thankfully), but is like picking a combination of Brendon McCullum's batting - only significantly worse - and Nathan McCullum's bowling. Never was going to be Test quality.
Bryce McGain - Probably the only one of these whose selection was actually justifiable (well, apart from being forced to pick Casson) given he had 2-3 good years behind him. And he still got belted.
Jason Krezja - Picking a big-turning offie who averages nearly 50 with the ball in FC cricket, after getting demolished by some hacks in a warm-up match does not bode well. I will admit though, it takes some serious skill to pick up 12 wickets against India and still look utterly ****. Not FC standard, let alone Test material.
Cam White - lol
Adding in another two to the list:
Brad Hogg - Crap FC record over a long period of time, picked on the back of desperation (mostly ODI form), and more use as a number 8 batsman than a specialist spinner. Stick to the white ball mate.
Nathan Hauritz - Picked from outside the NSW side, yet far and away the best non-Lyon spinner we had post-Warne. Says a lot about our system, when the best Test spinner in the country wasn't playing FC cricket at the time he was selected. Crappy FC record, but he could tie up an end and was technically pretty decent. Grew into his role until he was unfairly shafted for Xavier ****ing Doherty.
Sorry for hijacking, but raging/laughing at our ridiculous spinner selection policy is a favourite past time of mine. Compared to the guys we were trying and failing, you were lucky having Vettori. I'd honestly rather have picked Jeets than 3/4 of the above.