People answering polls have pretty varying views of what "Sharia" means, since that name tends to be used by any system of law that claims to be based on Islam. If you ask more specific questions, like whether a rigid Saudi Arabian / Wahhabist style interpretation of Sharia should be introduced in their country, support is much lower, though it depends on the country. One example: 60% of Malaysian Muslims believe that their country's current legal system is sharia, so when they say they support sharia, they mean the system Malaysia currently has, rather than a Saudi-Arabia or Taliban or ISIS style system.

>My assumption mostly came from the apparent extreme resistance Isis is facing in actually creating Sharia governance from the local power vacuums.

ISIS is not creating Sharia in the commonly understood sense. It's creating a Nazi-version of Sharia.

[citation needed]

If you really need one, then there are literally THOUSANDS of books and papers about Sharia, both about its theory and historical implementation.

I suggest you get a few (I would also suggest from respectable universities, not polemicists) and compare what they describe to ISIS.