If I was trying to develop good developers, I'd add a 7th initial, recurring step to the vertical: Talk to your customer as often and directly as possible to ensure you are still working on the right problem.

It seems to me that a lot of wasted energy is in the form of working on problems that no one cares about. Not that this is necessarily bad (hobby, fun, art, side projects, new ideas, etc), but in a concrete business setting you need to be a bit more aggressive about making sure the customer still gives a shit about what you are working on over time.

I find all of this leads neatly into the 2nd most important thing for me which is making sure you have a good domain model (schema). If the tables, columns and relations that represent the business are high quality and accurate (I.e., your customer understands them), the code that follows will usually go smoothly. Staying on the customer's heels regarding the applicability of your software to the business means you can keep this well aligned over time.

I think much of the tech bloat we see today is a side effect of attempting to outrun the complexity of the customer's specific needs. After sitting on the phone with vendors and customers for a week, you will likely not find yourself playing around with the idea of using some esoteric language or infra to implement things. It's incredible what being directly exposed to the customers can do for a developer's growth.