As long as those cards remain exiled, you may cast them, and your friends may cast them with your permission
I would actually argue that Armada Wurm is the more proactive of the two and that Centaur Healer is more of a sideboard card (though it depends substantially on the tenor of the metagame)
Exploring twice is extremely powerful, assuring a relevant draw or clearing out a couple of lands from the top of your library
In fact, Primeval Titan has been the face behind some of the most degenerate decks in Modern, starting with the Cloudpost deck that was prevalent in the initial days of the format, to the Red-Green Valakut deck, and then the Amulet Titan deck both in its degenerate form with Summer Bloom, and the more toned down version we see today with Dryad of the Ilysian Grove and Urzas Saga
The best dual lands for Commander differ significantly from Modern or Standard options due to card pool restrictions
It has earned its place in every deck that wields the power of the swamp.