For professionals, who work on OPE for a living, air power is the best choice. For owners, a top quality 1/2” cordless electric impact will work fine. 5/8” blade bolts are usually torqued to around 108 ft pounds. My 1/2” Dewalt has no problem removing them. In fact, it doesn’t have a problem removing the lug nuts on my F-150. Those things are torqued to 150 ft pounds. Try putting just a dab of anti seize on the threads of each blade bolt.I have a mz42 great mower but the blade bolts are really difficult to remove for sharpening even with impact wrench.