Re: NASA is a development lab
SpaceX itself was a massive gamble from the very start.
To says that 'all' they have done is evolutionary is probably true. And yet they are the only people to have EVER done it (ie reusability of S1). So whilst what that have done is evolutionary, what they have done to the launch market is revolutionary.
SLS is the same - its an evolution. As are ALL other rocket projects.
BFR will be the real revolution. And will be REAL heavy lift. Heavier than SLS but at a fraction of the cost. If it works, and I see no reason to believe it won't.