They are still different brands with different features and price points. The fact that a faulty part was detected on Bentley doesn't 100% mean a Seat will have the same issues
Yes-ish
However the differences are not as big as you think.
While this might be true for the luxury brands the "common" brands do share parts, often quite crucial ones too. (Think headlamps, think servos) Also they started to borrow design aspects from each other. They are not identical but certain lines do look very similar on a quick glance