1. referring to her as also a "rare class of pirate"
2. so he's still grouping them together.
Except that 1 doesn't necessarily mean 2. Doffy and Boa's being the same to a degree (rare class of pirate) doesn't contradict what I said.
For example, when male A tells male B ''we're both human (or we're both Russian/lawyer/activist/etc.) but I'm of a higher class'', do you think A is grouping himself with B even though he admits what they have in common (human/lawyer/etc.)? NOOO!!! A is actually making a distinction.
So Aokiji, whilst saying DD and Boa share certain similarity, ''praises'' DD by acknowledging he's an exceedingly rare class of pirate, that not even Boa is like him. Yeah, that's an indirect praise for Boa, too, but no doubt DD gets the higher place there.
we already concluded it was most probably due to the fact they are both "royals" and CoC users (nothing to do with actual physical strength)
Yes, I do agree Aokiji's words probably has nothing to do with physical strength or power level because he just said right before that what he meant. Did I say anything about strength?
And in the dialogue, Aokiji was talking about their being Shichibukai and king/queen of their countries. CoC is nowhere to be found. I don't even think it's of any importance here when there are several famous pirates who have it whereas there are only 7 warlords and only 2 of them are the leaders of their countries.