Just to throw out a meaningless benchmark, here are the percentages for my fort characters w/ the most PKs:

Ageryn: 5 out of 166 (3%)
Mizfara: 7 out of 110 (6.4%)
Kasir: 2 out of 74 (2.7%)
Denawe: 7 out of 72 (9.7%)

Now, only the last character was a mage. Mages are more likely to get rager fights, and rager fights are more likely to involve neutrals. Then again we can look at some Fort shapeshifters:

Hyzin: 6 out of 127 (4.7%)
Matedzuta: 9 out of 49 (18.4%)
Azidreth: 6 out of 45 (13.3%)

So Jerrokrar's 14 out of 43 (32.6%) seems to be well over the average for "PK competant fortress shapeshifters" (of which there have been very few, i.e. small sample size).