Well it's Sunday, public transport tends to start late on Sundays in Ireland (and the UK too - on many lines you can't get to London until 10am). Earliest arrival into Heuston being around 11am isn't too surprising.
You may have already checked but there could be an earlier bus/coach and it might even go directly to the airport?
yes, there's a decent number of direct services to Dublin airport - both private and public
if you're planning on travelling by public bus, I always book mine online beforehand, as passengers with reservations often get to board first
https://www.expressway.ie/