I think it's worth commenting on if someone draws an absolutely gigantic crowd - and likewise if someone comes onstage to tumbleweeds.
In the case of the latter - and really in terms of headliners poor SZA is the only ever example - it went viral and doesn't reflect particularly well on the festival if it becomes a regular occurrence. Acts - particularly from the US - aren't going to want to take a whopping pay cut for a gig that backfires.
However, the vast majority of headliners will fall between the two extremes and that's fine. Neil Young will.