Gotta play careful he's not the type to completely rush in and end the fight in 2mins IMO.
When using Mac the best way to describe how he works is like a boxer IRL, you take your time, get hard hits when you catch your opponent slipping, you take a step back and gain your composer rinse and repeat. If someone combo's you and you're at high % you can dish out the same within a few hits so you shouldn't worry about percent gaps.
I think people rush in for kills due to his immense power but doing this will lead into easy kills, Ganon is a perfect example of countering Mac due to his F-tilt knock back. Always stay in the center don't chase your opponent near the ledge the stage is your boxing ring.
Here's a video of a Ganon player knowing how to counter a run off the mill Mac player who rushes in, he countered Mac easily avoid doing this.
Skip to 25:40 and watch from there.