No team in the NBA gets to be a top team without getting lucky at some level. The current top team had good fortune that Curry fell to them in the draft and Green has been a huge surprise.
SA has the least amount of luck of the current top teams but drafting Duncan still required luck. They have been savvy about getting players like Parker, Leonard, and Ginobili, but there is some luck in that too.
Cleveland? They are lucky that LeBron came from Ohio, oh and let's not forget they got, what was it, 3 #1 picks in 4 years?
So yes, if the Celtics are going to return to the top, some luck would help. They need it. They just aren't that good as currently constituted (my negativity part). Draft picks are a crap shoot and FA signings often end up that you over pay and are disappointed. Trades are extremely difficult, especially trades that result in a home run.
The Celtics are due for some luck.