Elliot has "proved you wrong" in the same way that Franklin occasionally proves everyone wrong. He inexplicably scores runs when everyone else has failed - usually against ****ty attacks, yet never really puts us into winning positions. There's a big difference between saving NZ's face in a collapse, and actually building an innings to launch from. There's virtually no decision making you have to do in the former. The role is clear. You're not going to pick apart bowlers or put pressure on the opposition captain or lift the run rate at certain stages the way that real numbers 3 and 4 do.
The blueprint is that we have Taylor and Williamson to build us through the middle overs, but the only person in NZ even slightly capable of doing that job to the degree that they do it is Watling. There's literally no point in batting the way they bat if you can't do it as well as they do.
Asking Elliot to perform that role is asking way too much of him. He's nowhere near that good. If Taylor or Williamson go down, we have to completely re-think the game plan. If Elliot tried to do what they did he'd fail miserably and put pressure on the other guy.
Think this is way too harsh. Yeah Elliott's not All That, but contrary to your first point Elliott (unlike say, Franklin outside the subcontinent)
does score runs against good attacks and in live match situations. The inexplicability is more that he looks like a batsman some days and then other days is absolutely woeful, and this can be seen whether he's scoring ODI runs for NZ against Dale Steyn or almost getting dropped by Wellington for repeatedly failing against domestic bowlers. Since his 2013 recall he has:
1, 48 and 54 against South Africa (all live match situations)
22, 23, 24, 27 against England ('doing a Ryder')
71, 14, 3, 7, 4 in Bangladesh and that pointless tour of Sri Lanka. The 71 he built while the match was live but was last man out as the rest of the team collapsed around him.
Overall not great, but not terrible if you view the string of subcontinent failures as irrelevant to the World Cup in NZ/Aus.
In conclusion, this is far too many words to justify Elliott as my third reserve ODI top-4 batsman for the World Cup.