Second, Kherson in this scenario wouldn't be on "RU controlled side", because the premise is that Ukraine would drive it out
You really do not understand the logistical elements of the existence of a river in a theater of war.
That's fine, but please don't try to talk ignorantly of it. Major rivers create zones of control, and logistics barriers, and these logistics barriers are
absolutely vital in a war. Holding a river is a big deal and Kherson holds the river.
A major crossing of the river defended by a complex "surface" like a city requires a significant investment of troops and material.
If the UA can take it, they can launch assaults directly to retake Crimea, and the complexity of the city means the Russians can't really foil them short of burning the whole damn city. That's a big deal and means the Russians lose the war.