Sometimes you hit, but most of the time you don't.
Except sometimes you do.
The lottery picks are mystery boxes. Players like Rondo, Green, et al. are boats.
Boats that weren't taking the Celtics anywhere. Green, especially, was one whose outboard motor worked less than half the time.
I think the OP might not understand that if you have 1 pick in a particular range, maybe you have a 1 in 8 change of getting a long term contributor. If you have 2 picks in that range, you now have a 2 in 8 chance, more or less.
In other words, for any pick, you can hit or miss. More chances means it is more likely you get a contributor.
One major advantage of draft picks is that if they perform, they are incredibly underpaid for a few years. If they don't perform, that longest commitment you have to them is 2 years. After that, team options determine if they stay.
Also, you can trade a pick to any team, no matter their cap situation or their positional needs. This is not the case with actual players.
I tend to agree with Cuban when he said a few years ago that picks are overrated in the league, but I also shared a link in another thread that discussed the expected value of first round picks to a team's bottom line. And when Cuban said they were overrated, he is referring to picks as a means of acquiring talent through the draft. Their overall value is determined by the market, not by any kind of analytic analysis, since trade partners decide their value based on what they will give up.