I am not hung up on this 3 stars thing. Did the Lakers have 3 stars? They had 2 really top stars but you can't say they had 3. How about TOR in 2019. They had Kawhi Leonard and then a bunch of good but not great players.
I would definitely prefer to pair up Brown and Tatum with a skilled big 3rd star over a gimpy PG (Walker) 3rd star but the range of what that 3rd star can be is fairly broad, especially if you are really solid in your top 2. I don't think it needs to be Karl-Anthony Towns for example, although that would be nice.
It could be Collins I guess, even if it is still not 100% clear on just how good he is. Certainly there are others that could could fit the bill, Julius Randle? Andre Drummond? Nikola Vucevic? Rudy Gobert? Ben Simmons? How about Pascal Siakam (hard to say he is not good enough to be the 3rd star on a title team)?