Hi Gar,
I fly regularly to the US both via DUB and direct. If you are travelling on an ESTA + Visa Waiver, then I would allow 90 minutes to transit Dublin. Quite a few flights depart around the same time and you can hit it unlucky with the queue.
If cost really is not a problem and you can face a bit of administrative hoop-la, including a trip down to London, you can sign up for Global Entry which makes transit through US immigration painless, especially at the main airports:
https://www.cbp.gov/travel/trusted-t...united-kingdom
You need to check when they are doing enrollments in London as they only offer a few windows each year.