What you describe is very close to how hundreds of thousands of grads are hired into Indian software service industry. Aptitude test followed by training and plenty of time to come to speed and be evaluated. It has worked out fine for them. Layoffs are very rare.
Startups are a different story as time to market is crucial and you have almost no slack.
Maybe this is a problem with startup culture, perhaps technologists have it backwards.
In other industries , new startups seem to usually come from people with experience who have been round the block who have some idea of what is required to ramp up a company in the sector.
In technology it seems that if you haven't founded a company in your 20s then you have "missed the boat".
Startups are a different story as time to market is crucial and you have almost no slack.