Conducting 'independent surveys' under military occupation in an authoritarian state is a thoroughly nonsensical proposition. In Russia, it is literally a crime (incitement of separatism) to question Crimea's status as rightfully Russian[0].
I'm more inclined to trust nonpartisan independent Pew Research than your opinion. It's not the only independent survey either. There's also survey evidence from before the occupation.
Polls before occupation were in the range of 40-60%. If that's a good enough metric for conducting drive-by referenda under the watchful eye of heavily armed 'observers', someone tell the Catalonians and the Scots about this option (among many others).