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DA Polishers, with the right technique and right pad are very capable machines.
Make sure your technique is correct first- Medium pressure, slow arm speed, small working sections, over lapping passes, speed 6....
PO85RD (SF4500) is a VERY mild polish. Your Mercedes has hard clear coat so you will likely need a more aggressive polish (and might need a more aggressive pad).
I would start with something like SI1500 (PO83) with a 5.5 inch Lake Country Orange pad. Meguiar's pads are usually 7 inches which is a little too big to get the maximum performance from your DA.
After polishing out the swirl marks with the above combo, switch to a 85rd (SF4500) and a 5.5 inch white pad to burnish the paint to a super high shine.