What Lens Rental's chart could also prove is that more people rent those lenses more often so they tend to get beaten around more and those lenses are also large telephotos which are heavier and could also be beaten around in shipping.
It's not a very accurate chart to use to gauge quality unless they have a chart showing how often those lenses repaired are rented. Plus it's only data from one company. Borrow Lenses could have a chart that looks completely opposite to that.
The fact remains--Sigma is the most-repaired lens brand that they carry. And, counter to your comment that it might be that the large lenses get "beaten around in shipping", Lensrentals SPECIFICALLY states :
"Just because we get asked it a lot, Ill add that the Supertelephoto primes (300 f2.8, 400 f2.8, 500f4, 600 f4 from both Canon and Nikon) are our lowest repair rate lenses. Basically weve only had damage repairs for any of them."
Hmmm....so Nikon and Canon supertelephotos, all larger, all bigger than the top-four Siggys, are their "lowest repair rate lenses." Kind of shoots down the theory you've put forth
I've been involved with 35mm lenses since the early 1980's,and Sigma has earned its reputation. Did you see that neat-o post from a while back where the fellow's 70-200 Sigma just snapped at the lens mounting ring? No offense to Sigma, but their lens-building reputation is known far and wide as an "affordable" brand, not as a mission-critical brand. For light-duty use, and for bang-for-buck, Sigma offers good value. And yet, out of the lenses listed above, Sigma has 7 of the 16 most-repaired lenses...