I think Davis will not stay if there is no Irving.
If we trade for AD without Kyrie, we run the risk of investigating the higher chance that AD may not promise to re-sign in first person.
I also don't want feel comfortable giving the keys to Smart to run the offense 100%, and Brown still have issues with his playmaking, vision, and handles.
And yes, as you pointed out Hayward could probably not come back 100%.
So no, this team is not a contender.. Add Irving at PG, and yes that is a contender.
EDIT:
Brown, AD, and Horford are a great defensive big 3, and probably be our best players if healthy, but all of them lack the immediate ability to play make.
Horford can score on the fast breaks with intelligent passes, but I don't want him to consistently be doing that.