Definitely "more fragile" but they cause less damage to whatever they hit.

I had over 500 miles on both the bikes I built before I sold them and ALMOST no fender problems. I just removed them and went over the places where the fender brace connected to the fenders. I "reset" the rivets and coated the whole brace/fender union with JB Weld.

The one problem I did have was one of the rear fenders cracked where I cut it for clearance for the drive chain.

That was my fault.