Thats actually another pair of candidates for the top 20 list.
Both Ceasar and Magellan also have DF fruits that makes them extremely powerfull against anyone without extreme poison resistance.

As for Ivankov, well he? was able to defeat Sanji rather easily. Seems to be one of the leaders in the revolutionary army.
And fought Kuma to a standstil. The same Kuma who earlier trashed the pre-timeskip strawhat crew and made it look easy.