I don't think that acquiring George or Butler was realistic or something you can say "Danny messed up". Those would have been tough trades. Cousins seemed like a more doable trade based on what went down but that would have had another whole set of complications.
What I believe Danny could have done is a trade along the lines of Ibaka. Now CLE traded (or I guess signed but did a trade to open up a spot I think) for Bogut and that sure didn't turn out well and Ibaka hasn't made much difference in TOR so far (but probably will help them in the playoffs) but it seemed like he could have picked up a big without gutting our team or future assets.
I just think Danny is taking the long view. He did not want to give up any good future value just to win one more round in the playoffs this year. I suspect he tried many angles but teams just didn't offer the right deal in his mind. Overall, I am fine with that. I am looking forward to a team of:
Fultz
Smart
Brown
Zizic
BKN 2018 Pick
with a really good bench (Rozier, Yabusele, etc.), all on good contracts. Plus we can trade Horford in another year for other good young players.