Questions about example sentences with, and the definition and usage of "Vastly"

A: The city was vastly different today than it was years ago.
My Hebrew has vastly improved the past year. (I wish.....)
Joe was vastly confused about the situation.

You could say "greatly" instead. I think vast/vastly is used sometimes. I would not say I hear it often. The form "vast" might be more commonly used.
"There is a vast difference between Republicans and Democrats."

A: "Their economy is vastly Superior to ours"

"Culture can differ vastly from country to country"

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