If you choose not to pay the deflect cost when targeting an enemy unit, is the card still considered played for something like Ravenbloom?

Ruling: No, the card is not considered played. If you target a unit with deflect when playing a spell or activated ability, you must pay the deflect cost or the spell/ability is not played at all. You cannot use this to trigger "when you play" effects like Ravenbloom without paying deflect.

Nuances:

• For triggered abilities only, you can choose not to pay deflect costs. If you decline to pay, the triggered ability never goes on the chain (it's as if it never happened).
• This triggered ability exception exists to prevent feel-bad scenarios where players are forced to pay deflect multiple times on reflexive triggers (like Falling Star or Icathian Rain) and lose all their runes.
• Even if other legal targets exist, you can choose to target a deflect unit with a triggered ability and then decline to pay.
• For spells and activated abilities, deflect is always mandatory if you target that unit - you cannot decline to pay unless you literally cannot afford it (in which case the spell/ability is undone).