Point I made ~ the Greeks and Romans simply didn’t develop a good design for the Atlantic Ocean. They didn’t need to. They stuck around Mare Nostrum
Actually they extended the borders of the Empire whenever and wherever practical. It took a lot of farmland to feed the citizens on Eternal City. I agree with your point that they didn’t have the technology at the time because they didn’t need it. My original point was that if someone HAD made it back such a need would have immediately materialized. In which case, I have no doubt that Roman minds would have been up to the task of developing seagoing vessels.