I'm satisfied grouping Milne and Southee together as our 3rd+4th best T20 seamers. Milne is a good option, he hasn't done it for a consistent uninjured stretch at international level, but I think we'll see that if he stays fit. Southee has also received a fair bit of criticism for his T20 bowling, much of it justified and I'd still like to keep him away from death overs, but then we tried numerous others and they were all much worse. T20I seam bowler pecking order:
Ferguson & Boult
...
Milne & Southee
...
...
...
Jamieson, Bennett, Kuggeleijn, Tickner, Wheeler, others
That every other seamer we've tried has basically sucked is also why Neesham, who can bat and is still probably a level above those listed with the ball, is useful.