Let's be real: "0.01mm repeatability" on a desktop belt-driven machine is a marketing lie. What is the REAL tolerance floor?

I'm prototyping aluminum brackets for a robotics project. I bought a desktop CNC because the spec sheet promised 0.01mm accuracy.

Reality? I'm getting 0.05mm runout on circular pockets and chatter marks whenever I push the feed rate above baby-steps.

I need to hold an H7 fit for bearings. Currently, I'm forced to undersize holes and ream them manually.

Question for the pros: Is there ANY sub-$4k machine that actually uses Linear Rails + Ballscrews and can hold +/- 0.05mm reliably in 6061 aluminum? Or is this physically impossible on a desktop?