False!
Your assertion was:
"the only sure way to do it was by annexation."
I never said every other option, or ANY other option was iron-clad.
I simply stated the undisputed fact that there were other options, some of which could have resulted in a Crimea / Russia merger, that would have avoided the scorn that attends military conquest in the 3rd Millennium.
"when in fact Putin needed something dead solid certain."
piffle
What dire consequence would have resulted if Crimea retained its sovereignty for another minute, another day, another week, another month, another year, another decade, another century, another millennium?
"why did Putin opt for this scenario? Because it's Sevastopol in his pocket. guaranteed"
Your premise is your conclusion.
You prove to me Sevastopol would not have been Putin's if he'd used peaceful, lawful means. You prove that, then we can debate it further. UNTIL you prove that; you're just blowing it out your %$#.