I see this as a WebMD syndrome- every time I go on there, I am sure I have brain cancer, rabies, and the plague- I mean, just read the symptoms!
In realidad, as they say in my country, the danger from a grinding wheel breaking up and then penetrating a leather glove are pretty similar to you winning the PowerBall.
As Judy Tenuta used to say- "IT Could Happen!"
I own over a dozen 4 1/2" grinders, and have been using them daily for 35 years, and many times with a couple of employees doing it too.
We buy grinding discs by the dozen, and have NEVER had one disintegrate.
We do occasionally see a .045 cut disc shrapnel- but never seen one go thru jeans, much less leather.
I do wear gloves when I am grinding, most days. Leather drivers gloves is what we use- we have worn out hundreds of pairs of em.
The real danger is when some hotshot takes the guards off the grinder- those guys seldom get hired by me, but I have had a couple over the years. You can recognize em by the roadrash on their hands where they grind the skin off.
As the boss, one of my jobs is to but the guards back on, usually after I show them how you can do the exact same job, with the guard, that they swore needed grinding nekkid, standing in a puddle, with no guard, to be possible.
Anyway- if you are using thin cut discs, wear a full face shield, and a real shirt and gloves. For grinding, though, I really wouldnt worry about discs going thru walls and piercing steel toed boots.