I think it’s plenty good enough. As long as it isn’t so bad that it’s distracting (E.G. If Nick Cage tries to be italian.. or Leonardo tries to be Australian… ) then it’s fine.
Will is lookin a lot like Denzel in this movie.. but I can’t see Denzel pulling off the accent as well.
It’s not distracting. What will be more distracting is knowing what Dr. Omalu actually looks like and then seeing Will Smith. Sort of like Mark Wahlberg as Marcus Lutrelle.