Horses for courses.
The trend over the years seems to be to choose a lighter tool and overwork it. (For example, using the 3/8" drives when 1/2" drive should be used on the larger bolts.)
Thinking about it, most of the failures I've seen in the small grinders come from pushing them where the 7" or 9" should have been used.
The reason my DeWalt 4.5" has lasted so long is the 7" and the 9" are used for the heavy pressure/hard stuff. Yes, the 9" Black & Decker Wildcat takes a man to swing it for very long, but it's going to outlive me.
As an example, We were knocking the rust off my Studebaker truck frame. I was using the B&D with a cup wire wheel. My body guy was using a HF 4.5" with a smaller wire wheel. I worked all down my side and started back up his side before he was half way; about that time his HF let the smoke out and died.
Wrong tool for the job, but his excuse was when he's using them every day, lighter is easier at the end of the day.
jack vines