is the deliberate and systematic destruction, in whole or in part, of an ethnic, racial, religious, or national group."
The extermination of the entire group is NOT necessary for the act to be GENOCIDE. Germans in WW2 did NOT kill all the jews.
Killing BILLIONS of a given group is MORE THAN ENOUGH for the act to qualify as GENOCIDE.
Furthermore, I question your affirmation that cultural assimilation as encountered in our history is remotely similar to the borg ideea of assimilation who was more than once decribed as worse than death, a living hell.
Whether the paradox would have worked or not is not even relevant when considering Picard's choice.
When he made his decision Picard WAS CONVINCED THAT THE PARADOX WOULD HAVE WORKED
, and he KNEW THAT THE BORG WILL CONTINUE KILLING AND ASSIMILATING TRILLONS, that they are doing this even as he deliberates.
to condemn to death and assimilation TRILLIONS! Picard INTENDED to let all those people die when he could save them! Picard intended to sacrifice those people die without lifting a finger when he could stop it - staining his hands with their blood!
All so he could say he's the perfectly moral guy - so he can delude himself that he is so - you see, genocide was upon him whatever his choice; he could only choose who will die: a genocidal army which brought horror beyond human comprehension upon the galaxy or countless civilizations, sentient beings.
"Like I said, if you think committing Genocide is ok, that's your prerogative... however, I differ, and that's my prerogative."
If you admit genocide is monstruous, then you admit Picard's decision was monstruous, Praxius.
About the paradox's objective chances:
The fact that Picard&co were certain the paradox would have worked is strong indication the paradox's chances of dismantling the hive ming were very high.
Furthermore, weapons who shared significant similitudes with the paradox were used against the collectice later on - most notably on VOY:Endgame.
Plus, the exact conditions from 'I, Borg' were never ecountered again - having access to a drone classified by the collective as still connected to the hive mind without the borg knowing about it.