Does a controlled battlefield count as a base, specifically for effects like Yasuo's legend skill that move units between locations?

Ruling: A controlled battlefield does not count as a base. You can play units to controlled battlefields, but it remains a battlefield and does not count as your base for effects which specifically reference the base.

Nuances:

• You cannot use Legend Yasuo's skill to move a ganking character from battlefield to battlefield, as this would require the controlled battlefield to count as a base