Presented with those opportunities, I am absolutely certain the 2015 team would have wrangled a 7-10 point win.
Maybe. While the 2011/15 teams exorcised a lot of demons they almost always scored a try early and played with the lead most of the game, even vs the Boks they were up by the 50th minute. Sure they were calm as in the 2011 final, but but would have been the same if the needed 1 point in the final 10 minutes with Ellis, Donald and SBW as you 9-10-12? Doubtful.
Totally agree on the brain fades from senior players being the biggest difference. Not being switched on for the first two minutes was avoidable (especially after Twickenham last year), but the biggest blunder was the Whitelock penalty. Mo'unga kicks that and they are within 6 with 13 to go and it is all to play for.
The mantra needed to be just get within 7 and at least give England something to think about and potentially bottle it and you are probably right that is how the 2015 side would have played it.
I'm not sure if it is mollycoddling or what, but the same thing happened during the Lions series too. Absolute boneheaded plays from tenured players and Hansen is at pains to proactively defend them and would belittle the media for any even handed criticism etc. Less than 15 years ago Rodeny So'oialo and Stephen Donald were being strung up for bottling "friendlies" in far flung destinations like Rustenburg and Hong Kong. While some of the public reaction was puerile it did seem to have a reinforcing effect.