Why do you think that Robert Martin’ books are out of date ?
I don't think they're entirely out of date for all developers, but I agree with Sarah's assessment for juniors. I specifically instruct juniors not to bother with that material early on in their career, but highly recommend it to folks who are a little further along—as great reference material, with some parts worth ignoring.
It's not that the advice and techniques are all out of date, but for juniors it could be hard to separate the dated from non-dated. It makes sense that an older book which covers a lot of ground would not stand up entirely over time.
I'm not speaking for Sarah's reasoning, but this is my answer for your question!
So it's okay for junior devs to write bad code early in their careers?! What a bizarre attitude
It's important for younger devs to first write bad code to learn about why it's bad. I agree that the books probably won't be of much use for a starter because you first need to gather experience before you can learn from it.
You probably need to hire brighter devs then. The good 'junior' devs (hate the phrase) I've worked with no what bad code looks like already.
So if you want to go on a polemic level: why are your "brighter" Devs Juniors then?
Mire seriously, I would argue, you need decent experience to tell good and bad code apart.
It's okay for everyone to write bad code sometimes. Not everything has to be perfectly structured and totally optimised. 'Tactical' can be good sometimes, and technical debt isn't always evil - as long as you aren't blind to it and have a plan to get rid of it or pay down the debt. Pragmatism is a key element of remaining commercial.
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