Not OP, but I interpret "brand tax" as the opposite of the halo effect. FB's brand is tarnished, and arguably hinders rather than helps w/ IG brand perception.
There were multiple memes with screenshots of people declaring they were quitting Facebook and using Instagram exclusively. Don't know if this was widespread though.
Ah I see, thank you. I've also mostly left FB, keeping the account around only for events and messenger. It has become so cluttered. It really is on its last legs.