Affinity has two main balance problems: One, most affinity for artifact cards are colorless, so they can go into any deck
Queen's Agent Retrieval Agent Shardless Agent Shaun & Rebecca, Agents Sleeper Agent Spider-Woman, Secret Agent Tezzeret, Agent of Bolas Thoughtcutter Agent U.S.Agent, John Walker Unscrupulous Agent Vectis Agents Whisper Agent White Widow, Free Agent Wingshield Agent Xantcha, Sleeper Agent
The flavor of Universes Beyond sets has rubbed a bit too close to Magics a few times in the past
Decks with especially vulnerable basic Pokmon that can fall prey to direct damage may need a Manaphy, but despite what the feature from the official TCG's Facebook would say, it's not a no-brainer to put this meta call tech card in
And don't even get me started on the cards
Not content with mono-color land offerings, there are also some dual-color MDFCs that have a tapped dual color land on the back of a hybrid spell