Maybe on domestic issues that Obama had a say in, but blaming Obama for the Russian take over of Crimea is not comparable.
Obama's weak-kneed foreign policy -- especially his attempts at a Russian reset and then later appeasement of Putin (before getting serious way too late) did allow Crimea to happen.
We are the world's only superpower. Russia's taking of Crimea and their invasion of Eastern Ukraine in Donetsk and other areas wasn't something that Russia decided to do overnight. Putin tested Obama on quite a few different issues and in different areas before slowly building a plan to invade and steal territory. Just like how Putin is now testing Trump (intermediate missile launches), he tested Obama to see where his line in the sand actually was. After Obama's Syria red-line failure, Putin knew he could pretty much do what he wanted without much in the way of serious consequence (read: militarily).
But, to your early point, yes it is ridiculous to see many people engage in Whataboutism. Trump is measured against Obama in all things, or disparate situations are muddled or exaggerated to somehow draw a comparison to Obama. Obama was a mediocre at best President (I'm being very generous), and his prior actions and policies do have consequence, but the blame Obama for X, Y, Z crowd is rarely, if ever, laying out a defined rationale for why event X is a consequence of Obama admin policy (as I did with Ukraine).
Obama has plenty of blame, but the way to address that is simply as a reminder to the American people about why we are in a particular circumstance, position, or place. And, the GOP leadership/Trump should use it only as hindsight to say this is how we got here, but the buck stops with us, and here is our plan to fix it. But, of course, I'd be more mentally unbalanced than Donald Trump if I actually believed that will happen. Much easier for them to just to keep shanking Obama whether he deserves it or not.