I agree with you on a lot of stuff, but this isn't one of them.
The odds are always stacked against a player making it in the NBA. Even more stacked against being one of the best in the NBA. Being "ready" has very little to do with it. There are significantly more NBA caliber players than there are in the NBA that we never see because the circumstances don't break their way.
Getting drafted in the first round is the best way to get the circumstances and time needed to convince the NBA that a player is just a cut above all the other guys good enough to be there. Take it if it's there.
And let's stop with this fallacy that the NBA doesn't care about player development. They absolutely do, and take pride in it, and the existence and evolution of the D-League proves it. There are 5 ways teams can get better - the coaching improves, they draft better talent, they trade for better talent, they sign better talent in free agency, and their current talent improves. Teams aren't abandoning 20% of the path to competitiveness. They're just not.
I'm not sure we actually disagree nearly as much as you might think. All of the stuff in your post is correct -- NBA teams need to develop talent, getting drafted in the first round is key for these guys, and plenty of players are victims of circumstance. Agree on all three parts.
If I was boiling it down to its simplest form, what I was trying to say is basically two points;
1) I'm not sure making as much money as possible in the NBA (everyone's goal, for the most part) is exactly the same as getting the NBA as quickly as humanly possible.
and
2) As little as players or fans want to hear it, going to the NBA may not represent the best development path in terms of realizing your fullest potential.
It's fine to argue that the D League is there for developmental purposes but it is in it's infancy so while there are guys like Hassan Whiteside and others who have spent time there, it's tough to argue that it's really a strong developmental presence. In other words -- you really don't want to end up there if you don't have to (as opposed to baseball where even the best players go through the minors or the NHL where some players go straight onto rosters but the majority spend some time in the AHL).
What's more, the NBA isn't the NFL with 53-man rosters and taxi squads or MLB with 25-man rosters and with most teams going through 40 players or so each year. This is a league where you really need to do something to be a key rotational piece and carve out a 10-year career. You're not going to get a lot of time to figure stuff out b/c, as you point out, there are more qualified players than there are available spots.
So my suggestion is that if you are a guy with elite physical tools, being really good at basketball before you head off to the NBA could help you increase your role at that next level and, therefore, increase your value and contract $$. So a guy like Tyler Ennis goes b/c his stock isn't likely to get any higher? That makes sense. A guy like Jeremi Grant goes b/c he is fine with being a 2nd-rounder? I'm fine with it, but if I were advising him, my thought would be take the opportunity to get better offensively when you're getting a ton of touches and playing 40 min/night for 35+ games and however many practices and scrimmages. I find it hard to believe he would have dropped further if he actually takes a step forward offensively. Meanwhile he's facing a major uphill battle for shots at this point.
Does coming back to college guarantee anything? No. I just don't think that decision is nearly as cut and dry for the guys like Grant, Fab -if he's still going to class (RIP), Malachi, etc.