First vs third person: Making the change feel significant

I keep envisioning a game where a third person perspective is an advantage, a power-up which costs resources and/or can be taken away if the player's 'external eye' is targeted and destroyed by enemies.

But then I think about the Elder Scrolls games, where switching between these viewpoints is just a matter of preference. It costs nothing and has no specific vulnerability.

To justify a third-person 'power-up,' I'm thinking it would need to be more like the Spies vs Mercs mode from the Splinter Cell series. Spies use third person because getting spotted can have severe and immediate consequences when you're perpetually outgunned; the first-person Mercs pay for their superior firepower with reduced situational awareness so that getting flanked can have severe and immediate consequences.

Does that mean that a game needs an unforgivingly low time-to-kill to make the most of this mechanic? (or an otherwise strict fail-state like 'the target vanishes if they spot you')
Does it fall apart when we start letting both perspectives use the same weapon loadouts?

Alternatively, perhaps first person has more fine motor control, and third person has wider area control.

What do y'all think? Anything I've failed to consider so far?