So we are comparing attitudes are we? Both Southee and Boult know the team relies on them with the new ball, and they need to have energy left to fully utilise it come the end of a day and more importantly not break something. As opposed to Wagner and Bracewell who are there to bowl themselves into the ground. If say Henry was opening the bowling with Southee at 3rd seamer, and Southee was reluctant to bowl, then this would be a valid point. But its not, similarly for Anderson, he still has injury problems and needs to make sure he can still bat come next innings.
Right, but when you're not taking wickets with the new ball you become an absolute liability if you can't bowl a good set in the middle overs.
Southee - amazing, he can come back and make stuff happen with the older ball.
Boult - only really creates opportunity when the ball is absolutely new.
Wagner - has a tendency of taking big wickets and taking them in stages of the innings that we struggle, due to not having good spin bowling.
Now, the argument was never "is Southee better than Wagner" - that was the strawman constructed to try and argue the real point, that Wagner is well known for his ability to make the old ball move and statistically, has a much higher likelihood of taking wickets during the middle overs than any other NZ bowler in the last three seasons. Going back further than that isn't beneficial, because we end up with Southee who was extremely inconsistent and it's just too long to understand where the bowlers are currently at.
Anyone disagreeing that Wagner doesn't get reverse swing - fine, but the basis of evidence indicates not only does he get reverse swing but it's something the selectors think about as a main weapon he brings to the table.
Anyone disagreeing that Wagner doesn't get reverse swing, then trying to say Boult gets more than he does - flat out, unbelievable statement and something that has no basis of reality.
You'll also note I've stated I think we should be playing Wagner, Boult and Southee all together irregardless, because we've got more chance of them being in the side in three years time than we do of Sodhi or Craig based on their performance history ( domestic and international ) -but we're stuck in the same trap that almost every side since the 80s has been in when they tour spinning nations - let's select inferior cricketers because they happen to bowl spin and ensure that we have no threat/danger and don't get our more established peformers an opportunity to learn how to operate in foreign conditions.