Weve seen multiple types of unique counters placed on players: poison, energy, experience
While both of Yuna's abilities can be played for value, her second ability leans into the graveyard for extra utility and resilience
Furthermore, it has two unique markings that make it valuable
Uncharted Territory, like Metallic Mimic, is a card that supports tribal decks of all stripes
Overall, Planar Portal is a slow, value-oriented political deck with lots of card and mana generation to support its weaker color identity.
Although it may sound like a bit of a tongue-twister, the cost reduction that comes from tapping a creature is an additional cost that's part of harmonize's alternative cost