Inheritance is slowly fading away in favor of composition. Drupal is an absolute abomination when it comes to extending classes, as in 5-6 in the chain is not

Inheritance is slowly fading away in favor of composition. Drupal is an absolute abomination when it comes to extending classes, as in 5-6 in the chain is not uncommon. However, Drupal was never called for its high modern code quality either. Projects like Symfony favor Interface model (the I in SOLID), and recent versions address some of the pain points you mentioned. In terms of analyzers, I rely on PHP Inspections EA plugin for PHPStorm (commercial IDE). PHPStan, Phan, and Psalm are the three most popular PHP static analyzers and they are getting so good!