Okay, I did a two part experiment on this. Let's just say I'm not going to be using any brazed on eyelets for rack mount use. Hourglass or bottle cage mounts should be fine. The eyelets I used are thick, so bending them would be pretty difficult.

I had a piece of angle iron and brazed on two eyelets. One was just cleaned up, no filing. The other, I filed a shallow groove. I held the other leg of the angle iron and beat on the eyelets on their sides. They both broke off with a few hits, not really that much difference, 4 or 5 maybe?. Then I noticed there wasn't full penetration on the grooved one, so I brazed another eyelet in the groove (should go find the two first victims). This time the eyelet bent over fairly far before it broke off.

My conclusion is you need more surface area.

Having said all this, most eyelets would never see loading like this and would work fine for years. Unless it got hit wrong.