True I put a big number with 10 a month, myself I have lost 2 Mackinaw to ganking in highsec since 2012.
For exhumers, losing 2 Hulk is enough for a Orca btw, and I see them going down at least 2 a day in highsec on calm days.
The thing is, blinking is enough to lose a covetor to just one lone catalyst, while you really need to make multiple mistakes in a Orca (not putting tank, mining in a FOB infested system, getting suspect, etc.).