are brake dust shields necessary

Yup, right after they P graveled some of the roads around here. Wore a groove in the rotor, had to replace it.

And I'd bet you had "dust shields" on at the time.
So how are they ever going to keep dust out? right?
Best thing they have ever done for me was to keep a pressure washer from blowing steering parts grease all over the rotors. :D

Well, and maybe a few rocks that it kept out that I never knew about.

Otherwise I would rather the discs had more airflow instead of being covered over with the shields on the inside.