Yeah the cracking leg thing is a bit much but based on what we've seen/what we expect from them this isn't that crazy
People have to remember that these are the WGs replacement for the Warlords
Even without haki, experience, etc they're still considered (by Fujitora as well as the WG) suitable replacements for some of the strongest fighters in the verse
Mind you, Vegapunk and the World Government chose to use Lunarian DNA and mix it with Warlord DNA instead of replicating King
It's clear that they're meant to be above regular Lunarians... somehow
This is Sanji (low YC1 - YC2 level) plus Franky and Robin (neither of them know haki and Franky is the only one with high enough AP to matter) plus 2 tag alongs (Usopp and Nami can't do anything)
I'm not really surprised
Especially when even Blackbeard was shocked when he saw them