I think Sun's overall back row play and serve-receive have already improved a lot since being at Nebraska. She looks more comfortable defensively and is digging balls that usually bounced in front of her at Texas. The training is definitely part of it, but I also think Cook let her play through her lows in the back row/serve-receive instead of taking her out (which Elliott did) even though it cost them some matches IMO. I think she's prone to have breakdowns in her game, but Nebraska's overall team defense will overcome those deficiencies.
Elliott's tenure has produced some dominant front-row college players but in the 18 years he has been here, none have really been true passing, six-rotation players except for Mira Topic, Ashley Engle, Sha'Dare McNeal, Amy Neal, and now Micaya White (who is still too inconsistent at times).
With the college rules of allowing 15 substitutions per set, Elliott has made his success by getting big, high-jumping, hard-hitting pin hitters like Hooker, Faucette, Webster, Eckerman, Bell, Prieto-Cerame, Nwanebu, and Bedart-Ghani who only played front but didn't have the skills to play in the back row. (Hooker didn't have the opportunity to develop b/c of Track&Field and Nwanebu b/c of her chronic back injury). Thus, Texas gets labeled as getting the top athletes but not the top volleyball players....
It would be nice if Elliott could develop complete players but at the minimum, his focus in the upcoming season should be improving the team's overall serving and floor defense.