Uneven wear / grooves on rear brake discs - Octavia vRS

Hello

I'd like to get a second opinion and whether someone else here has also encountered something similar.

I have an Octavia vRS with ~6600 km total mileage. I've noticed that there's uneven brake wear and grooves on the rear discs. I did contact the local dealer about the issues about a month ago. They inspected the brakes (but didn't do anything) and suggested to do a bit of harder braking from time to time to get rid of whatever dirt / rust / debris that might be stuck to the pads or discs. I've done that that but there really hasn't been any effect (still uneven wear and grooves on discs).

Has anyone had a similar problem with the brakes on their rather new car and if yes then how did you address this?

Should I bothering my dealer again about it to sort this out or I shouldn't really be worried at all?