I've mentioned this before, but in my opinion, the most straight-forward way to become a contender is to draft a star, sign a star and then trade for a star. The issue is that most people get hung up on the belief that they need to draft a franchise player, then either draft or otherwise acquire the other stars. The part you highlighted was basically saying that you can't sell out to get a franchise player, because you'll be so bereft of talent that that player will want to leave. Rather, it would be better to draft a second banana, sign a third and then trade for a first-banana.
This doesn't mean you pass up on franchise players if one falls to you. In the context of my whole post, what it means is you need to worry about drafting tradeable pieces rather than taking risks on stars all the time, because ultimately you're going to have to be able to acquire one or more stars from outside the organization, and a bunch of busts that had a 10-percent chance of becoming unicorns aren't really good enough for that purpose. In terms of A), B) and C), it doesn't mean you don't take A) guys when they're there. It means you should value C) guys more since they'll be useful to get a star if they don't develop into a star themselves.
To borrow the common baseball analogy, many of the historical high-scoring teams didn't get there by just hitting a ton of homeruns. They got there by being able to get on base and advance through hits, sac-flies and stolen bases. The Rangers from the WS runs are an example of how that looks. Anyways, in the Spurs case, getting solid-C assets and being willing to move them to get B and then A assets is critical to being able to spec into a contender while avoiding tanking. That's why they have to be willing to move guys like Murray and not cling to them because "He's youngish and not horrible, so we have to keep him". DJM, White and hopefully Johnson were really good picks for their position, but then you have to be willing to trade for better picks, out-draft that higher position, develop them, trade them for higher picks and grab those A) players. Otherwise, you end up getting cap-locked into mediocre players that you're hesitant to upgrade over because you've convinced yourself they are core players.
So a possible plan right now: Bank on White being the third banana; sign Collins; make a trade for a guy who fits with them but his hopefully better than them. Another: Trade for Sabonis; sign a guy like Trent with the cap space; hope you kept enough value to make an all-in trade on a star wing. A third: Trade Murray for draft value; sign Collins or another PF if a good one doesn't fall in the draft; develop around that move balanced core while keeping a max slot open for 2022; In 2022, hope you already have one star before signing and trading for the others.
What you don't do: Draft a one-in-a-million guy because he kinda looks like Giannis at 18 or whatever; get rid of any decent vet to give minutes to young players; hang onto decent ones with your cap space; hope you get a high pick to take a shot the next year. That's the kind of path a lot of posters seem to think the Spurs HAVE to take because they aren't a free-agent destination. It's antiquated. You don't have to worry about signing stars if you're going to trade for them, and the thing that attracts free agents the most is playing with other stars. The thing that repels them the most is being a ty team in a small market.