You compared your stitch outs comparing your MB4 and the MC12000. I don't have a MB4 but I do have a commercial 16-needle Melco Amaya XT. Needless to say the Amaya XT has a higher stitch quality than my BERNINAs, Pfaffs, Vikings and the MC12000, since it is a commercial machine.
For comparison, I stitched out the same design on my MC12000, BERNINA 830 Limited Edition and my Amaya XT. All machines were set to embroider at their highest speeds, the BERNINA 830 LE and the MC12000 at up 1,000 spm and the Amaya XT up to 1,500 spm.
The BERNINA 830 Limited Edition embroidery stitch quality was close to the quality of the Amaya XT stitch outs and was noticeably better than the MC12000.