I suppose in the vernacular, an elected government can be said to "seize power."

They won a majority of seats on the Palestinian Legislative Council, not a mandate to rule Gaza.
They achieved that through a violent coup.

That said, Israel would never lift the blockade anyway, as any serious observer would notice.

They have eased it considerably.
They used to prohibit building materials because Hamas might use them to build military infrastructure, and they did.

Gaza declared war and Israel declared a blockade as any country would.
The difference is that most countries would apply a total blockade against a belligerent, not just an economic one.