As far what numbers tells us? I'd say no. No alliance raids in this game that justifies the need to bring in 2 healers as none of them dishing out enough incoming damage to overwhelm any healers' output.

Imho, the existence of 2nd healer is a mere foolproof in the event 1 healer is simply prone to making bad decisions that costs their party several deaths & potential wipes; even moreso if the party is filled with clown fiesta. A 2nd healer can easily mitigate that. In a pug setting, that will be either handy or downright unnecessary.