re: LSU should have taken its time.

Well IMO he was a risk because you really aren't sure what you are getting. By backing out of his agreement with LSU (rumor) he wanted the highest bid with a 5 year or more deal and that was too much to gamble on.
Hiring Ed O LSU can reasonably think the recruiting will remain at a high level, keeping Aranda keeps your D at a high level (as long as hr signs) and bringing in a top O coordinator will keep the team very competitive. If things start to come apart you can move quickly to your next head coach and hope better options are out there at that time.
Lot of if,s but still reasonable to think it may work out with Coach O. Best option for the powers that be at this time, in their mind.