I wonder why nobody mentioned it - there is one more advanced principle AHA: (Avoid Hasty Abstractions) https://kentcdodds.com/blog/aha-programming#aha- Overusing the DRY principle can make software almost unsupportable.
Yes, IT processes significantly differ from those in other areas and can't be evaluated by the same methods - due to the complexities, hidden problems, and overevaluated expectations. For example, the known fact: adding a new member to a team doesn't linearly increase productivity.Nowadays probably AI will help here :)
There is also more advanced AHA principle (https://en.wikipedia.org/wiki/Don't_repeat_yourself in alternative section) - which is an evolution of DRY and is great for avoiding redundant complexity caused by DRY.
There are few factors why PHP popularity is decreasing, not because it is really bad. But very often other languages build its popularity on promoting how "bad" is PHP. It is also no longer fashionable as it was in the beginning, but other language promoted as such. And more.. So, I think, rebranding and good marketing could help here.
Don't think that there are many headless CMS that has better content models than Drupal. Basically Drupal has entities, bundles, fields, all can be stored in yml configs and it can be easy extended. Could you please provide examples?
That is just because you worked for long time with backend. Angular looks better for you - because it was developed to be easy adoptable by backend devs. But React is great, it just use different paradigm than is used for backend development. PS.I have also stared from those web early times.