Amperage is not the only factor for “heavy duty”.
Well designed and well built motors can sometimes produce more or less actual power than the Amperage or Watt rating on a grinder’s label specs will indicate.
There have actually been tests in magazines were maximum motor torque was tested, and lower amperage rated motors sometime came out ahead.
As for grinder failure, the most likely things to fail, are the electronic units such as variable speed modules, which can be costly to replace, especially with some European tool brands.
Even some non-variable speed grinders, particularly those made to European Industrial specifications, will have safety electronics built in that can be as likely to fail.
Brushless motors don’t have the brush issues, but they do have the potential electronics issues the variable speed grinders might have.
While most “brushless” grinders are cordless, Hitachi/Hikoki/Metabo HPT does make some gronders with brushless motors, that have comparatively narrow grips compared to most grinders, which is the reason some users like the models.
If you want to avoid the potential electronics issue, and save money, simpler grinders like some of the Cheaper models, like Black & Decker, will likely not have the fancy electronics.
Older US made geinders almost never had the specialty electronics, including old Bosch, Milwaukee, Dewalt, etc. models.
Porter Cable used to own Flex Tools of Germany, and offered angle grinders that were made in Germany, but which lacked the safety electronic modules that the same Flex models had. The PC were also 40% cheaper in cost or so.
As has been mentioned, the detachable cords some tool manufacturers use can also cause reliability issues.
Most designs I’ve seen however can probably be rewired with a strain relief and permanently attached cord.
