Luffy is a paramecia and his bounty is 300 milion berries, if DoFlamingo is one I won´t be impressed by it, his power is very dangerous, he can control the most powerful member of a crew or the second one and kill all them.
But the power that a lot of people is ignoring is the Aura/Spirit power that we have seen in Zoro and Shanks, this power is the only one that can damage Logias and surpass Blackbeard Devil Fruit, this is why Whitebeard crew believes that Shanks is dangerous for their captain, he can hurt him.
In other words, we can have the next distribution in the Shichibukai:
-Logia
-Paramecia
-Zoan
-Giant
-Fishman
-Swordman
-Aura master
They are experts in their devil fruits and habilities, no one can surpass them in their mastery but this is not like saying "they are the strongest here", for example Mihawk could be the strongest swordman of the world (his habilities with the swords isn´t surpassed) and be less powerful than Jimbei.
And the Yonkou?
I believe that they combine powers, for example Shanks has the hability of a Swordman and an Aura Master but he is nos the master of one of his habilities, Whitebeard could combine the giant strenght with a Logia fruit and the other two have similar combinations. The problem with my theory is that this puts a Fishman with a devil fruit and this is dangerous for them unless he has mastered it until the point that he can swim without being affected by it.