Nah, it doesn’t assume every pick they make will hit.
Do you know how many 1st round draft picks they own for the next few seasons? They could draft players or use them in trades. They could flip those picks for more picks further out.
The point I made was they have flexibility and multiple means to keep a contender for a long time barring something totally crazy happening.
The funny thing about all of this is what they are doing isn’t something new or ground breaking. I literally watched my Spurs be a playoff team for 20 straight seasons doing something similar. You find your 1 or 2 stars and continuously build around them with cheap contracts, via the draft, undrafted free agency, or waiver wire. Dont over pay for marginal talent or role players.