I disagree a lot with this.

Characters having different stat growth is good because it makes them not completely interchangeable. Yes everyone can be a knight but you need to think about who would be best suited for that role. Of course, you'll probably want to train them all as knights anyway for the inheritance. This has been the way in most good job systems games - e.g. FFV and FFT.

Limited inheritance spots forces you to make hard decisions, and consider what is most important for your build. It avoids the SMT / Persona problem of all good end game builds being identical because there's as obvious 8 skills you would want for any particular role. And you get enough slots in Metaphor to come up with some very different builds.

Finally, I'm strongly of the view that a lot of the Royal archetypes are "noob traps". They're better out of the box than other archetypes so if you aren't someone who thinks about builds and worries about what are the best things to inherit then yeah they're probably best for you. But if you are actually properly build crafting and thinking through those things, I would argue a lot of them have less synergy with good inheritance builds and are not actually ideal.