Just re: Santner, I've gone back and forth with people many times (I was doing it recently on reddit ffs) about how he is misrepresented as a bowler. This is not so much about his actual likely performance, more just the attributes he possesses.
I know I'm not alone in this view among CW nerds - I've never agreed with this idea that he's just a "holding bowler" and I think he pretty visibly has the attributes to take wickets in turning conditions. Most importantly, he gets bounce and contrary to popular belief he does spin the ball. He is capable of flighting the ball and getting it to rip, and also of darting it in and getting it to either slide on or turn a bit, in a vaguely Jadeja-ish manner.
The issue is not his attributes or lack thereof, rather it's the intractable issue that he will never get the reps in to hone this style of bowling. He didn't start his international career with a weight of FC wickets behind him, he's stuck on the international treadmill, his style of bowling is unlikely to be particularly effective in home tests, and he hasn't previously done enough to demand ongoing selection in our away test side. These are just facts of life, and I'm certainly not suggesting he has been hard done by in selection - actually I'd say our selectors have been relatively indulgent with him. I just think it was always conceivable that he could take bags in the subcontinent, not by coming up with a doosra or whatever, but by constructing spells of bowling using his existing attributes in a way he hadn't previously done.