I don't think that accurately reflects the situation.
You're right in that not everyone makes it, but you keep as many as you can as long as you can to maximise your odds. You then need to be good at identifying talent within and without of that group.
The Warren and Tim show just signed them all up to overs too early, on too-high a tier contract (often with guaranteed Top 30) and hence we've found ourselves trying to dig out of it for the last few years.
It is THE reason why depth has been an issue. There's no room for decent replacements because those who have been available in the squad when needed are not even in the conversation about being ready, much less ready to step up and do a job.