It is, but it’s going to be really hard.
For instance, a healthy Kemba, Hayward, and the Jays would have been at least a quasi contender.  But, our luck with health has sucked.
I think we need the Jays and probably four above-average players.  In theory, Williams and Smart can be two of those four, particularly if Marcus is a 6th man.
Ideally, we’d need a top-15 PG and another top-15 starter.
But, to look at how hard it is, let’s give us two good starters, without losing any of our core:
Timelord
John Williams
Tatum
Brown / Smart
Brogdon 
We can’t ask for much more than that.  In fact, it’s probably unrealistic.  But, is that team a hands down contender?  Probably not.
Did you mean John Collins?
Yes, but with John Williams games would definitely have a more epic feel.