Why did the 4 ranks per career put you off?
Because it encourages you to do the boring thing, which is continue in your career. By having every class have four separate ranks you effectively have a class-and-level based system in the style of D&D 5e where the default the game points you at is you continue in your class although it's
possible to break out of it the way you can multiclass in D&D 5e.
I don't actually expect this to change the experience of anyone who's been playing previous editions because how you learned to play matters more than how the game coaxes you to play. But I would expect any new WFRP 4e players who pick up the game out of nowhere to not just advance their career about as often as 5e players multiclass. And game and setting alike are harmed by this default expectation of play.
Plenty of the careers in 2e had multiple ranks anyway, they’ve just given that option to everyone without taking away variety?
Not that I recall? (I can't currently find my copy of 2e). The ones that
had multiple ranks were ones that for specific reasons you weren't supposed to break out of; wizardry's the study of a lifetime, priesthood is a calling, and being a Slayer normally lasts for the rest of your life.
And e.g. a Tier 4 roadwarden just feels
weird as a concept, while a Tier 4 ratcatcher in WFRP isn't an expert in hunting rat-rats but something that officially doesn't exist that's likely to say "rat-rats", and as such should definitely have a different class title and probably multiple explicit ways in.
And that the WFRP 4e designers chose to make this change that feels as if it harms worldbuilding in two directions and will harm the way anyone coming to the books cold is likely to play the game gives me
very little confidence in changes they made elsewhere.