I used a Dewalt 11 amp in my welding shop, got used every work day before I retired. Sometimes some very heavy duty grinding. The average life was around 5 years in my welding shop, before the cord got killed, or the brushes wore out (you used to be able to get brushes, but it was getting harder to get them 4 years ago). I also can't speak for what they are selling these days.

At the welding shop, the 11 amp motors had a longer life cycle, especially if your doing a lot of grinding. The smaller motors would slow down on rpm the longer they were ran without a stop. The 11 amp grinders are a bit more heavy then the lower amp motored grinders, you use both hands with the 11 amp grinder, but that also gives you more control.

I can also tell you the grinding wheel you are using makes a big difference as well, the cheap wheels put a lot more dust into the air, and they grind away a lot faster then the higher quality grinding wheels do. A higher amp grinder and a good made in the USA wheel will be a different grinding experience then a china grinder with HF grinding wheels. The more you grind, the better you will understand. Gene