Yes you are eligible for EU261 — there was a ruling earlier this year that enforced EU261 all the way to final destination in the US, not just first point if entry.
Because of this you are eligible for the full €600 (instead of the smaller amount if it was just the 2.5 hour delay).
I haven’t filed under this new ruling with DL yet but I did with UA earlier this year and it was resolved (was offered either €600 or $1000 UA eCredit) so should be similar with DL.
Submit a complaint and lead with your request for EU261 and note that you arrived at your final destination greater than 4 hours after scheduled arrival so are requesting €600/person