I wonder how much it matters that most of our guinea pigs are not purebred. I can see there being more of a propensity to illness if animals are selectively bred for specific physical traits involving potential inbreeding. However, I suspect that none of my pigs were bred deliberately for anything in particular. My aby was likely not a 'full' aby, my two long-haired pigs are obviously crosses and not purebred shelties. Sundae looks like a standard short-haired pig, but again I have no clue what her background is, and she could be carrying genes that aren't expressed.
Thus far out of my pigs, Linney (sheltie cross) was very healthy and lived to be six with only a few issues (a couple of bladder issues, an infected cyst removed from her back.) Sundae (short haired) has had the most issues out of anyone, with chronic bladder problems, some dental and dental abscess issues, though at almost 5 she continues to do well and not let her issues get her down. Frenzy (aby) died at 18 months of sepsis following a dental abscess, but again, she may have survived with more aggressive care (the vet I had at the time was not very up to date with his guinea pig issues, but I was a new owner and really didn't realize.) And Hadley (sheltie cross) is too young to know just yet.