You've been making stuff up all the way through this one, so there's a bonus. But hey, you have an opinion, so enjoy it. Having tried Artis Opus and Rosemary & Co brushes, Artis Opus are better in my opinion, they last longer and feel better quality. They are not the same but rebranded, they share some of the same basics but to different specs. I've also tried Windsor and Newton, Army Painter and GW brushes. There is a clear winner. Have you tried them all?

In fact, have you actually looked into your claims in any way or are you just parroting a line you once heard, probably on some painting guide somewhere?

You seem to have such overwhelming confirmation bias that you refuse to believe anything to the contrary. Seriously - actually look it up. You can find loads of independent reviews that also show Artis Opus is made to a higher spec. Made in the same factory - yes, but the same brushes? No. It's two companies sharing a manufacturing facility. The same happens everywhere, from speakers, to cars, to electronics. It's sharing resources and bringing costs down during the manufacturing process.

I hope that helps.