In the practical art of war, the best thing of all is to take the enemy’s country whole and intact; to shatter and destroy it is not so good. So, too, it is better to recapture an army entire than to destroy it, to capture a regiment, a detachment or a company entire than to destroy them.
One cannot use nuclear weapons to take and hold territory.
You also say:
Conventional military is entirely useless except for proxy wars and small-scale meddling in non-nuclear states’ affairs (e.g. the Vietnam or Afghanistan wars).
But another way to say that is:
“Conventional military is useful for proxy wars and small-scale meddling in non-nuclear states’ affairs.”
—Sun Tzu
One cannot use nuclear weapons to take and hold territory.
You also say:
But another way to say that is:
“Conventional military is useful for proxy wars and small-scale meddling in non-nuclear states’ affairs.”
The United States does these things quite often.