Michael Dorn isn’t exaggerating there, as Star Trek: Discovery videos have shown the eyeballs are about the only visible facial feature on Mary Chieffo once she was fully suited up as L’Rell.
In spite of that, there were few complaints about Chieffo’s portrayal of L’Rell in Season 1 of Star Trek: Discovery and her facial expressions seemed far less limiting than Dorn’s statement would imply.
It is fair to say her face is far more hidden by makeup than Dorn, who had his eyes, cheeks and mouth largely untouched by the Star Trek team when he played Worf.
At the end of the day, Dorn doesn’t have to worry about it, especially considering nothing we’ve heard about Season 2 involves him making a cameo.