The maximum number of upgrades for WS and BS for a witch hunter captain is always 6 for WS and 8 BS regardless of whether it was your starting captain or an upgraded zealot. This means that the starting captain's max stats are WS 60 and BS 70 (all other captains are 60/60) so I think the witch hunter starting captain's upgrades should be 6 for WS and 6 for BS like other human captains. But it's possible this is just witch hunter flavor and they are meant to have 5 higher ballistic skill than anyone else can get to, and it might not be a bug. The other problem is when your captain dies and you upgrade a zealot to captain. Because he still only gets 6 upgrades for weapon skill, his max stats are WS 55 and BS 65. I'm fairly certain you didn't mean for the Witch Hunter Captain to have the same max weapon skill as a ghoul, and be 10 behind everyone else in the game. So I'm pretty sure that one's a bug.