I don't really care if Brown is a #1 option, #3 option, or whatever. All I know is that this kid is 21 and already has the capacity to shoot the 3, drive and finish at the rim, and defend like a maniac. Holy moly, he has the chance to be an absolute terror for the next 10+ years.
Amazingly, we might actually be underrating Hayward and Tatum. It's hard to remember, but Hayward was an elite wing last year. He was not some fringe all-star, he was a superb scorer and good at pretty much everything else. Even if it takes time for him to come back to 100%, the expectation should be that he's going to be 2nd to Kyrie in terms of being a primary scorer and primary ball handler next season.
I kind of feel similarly about Tatum. He'll still be young, but just think about what he's already shown us this year. Add a little bit more muscle and a whole extra year of training and experience, and look out.
It's easy to sound like a homer, but think about this: arguably the two most important things you need in the NBA playoffs are 1) the ability to create one's own offense, and 2) the ability to switch on defense. The Celtics will have that in spades once they get Hayward and Kyrie back next year.