Is there a better way than twig files overwrite? In my project, I have a " field--node--title.html.twig " file, I used this file to overwrite the title label to be able to give it a certain class.

I know you can be more specific using " field--node--title-x.html.twig ", Where x can be a block or a page!

I was wondering if there exists a better way of doing this. Maybe I could do IF conditions inside " field--node--title.html.twig " file to check for a certain block or a certain page. 

This would be much easier and it would also decrease the number of files in the field folder in templates.
Yes, usually there is a better way: preprocess functions allow you to alter the render array that is passed to the twig template. Adding a class is, in most cases, possible, but you might need to check how the twig file is turning the render array into markup.

This article has more info: https://www.drupal.org/docs/8/theming-drupal-8/modifying-attributes-in-a-theme-file