For the second part of your question.... Uhh... no. Not even a little bit.

Because guns.

Miniaturization of military technology has been a thing for a very long time. That is, things tend to start out large and gradually become smaller.

Which is to say, Navies have had guns on ships longer than armies have had riflemen. Though not by much.

But, lets take guns out of it for a moment, because they came in relatively late in the Medieval period, and for at least a good chunk of that period there were not cannons on ships.

But they DID have the springald, the mangonel, and the trebuchet.

As well as ships that were, on average, larger and more maneuverable due to improvements in sail technology and navigation that continued throughout the middle ages.

What the Classical period DID have, was NUMBERS.

Lots and lots of numbers. For example: At the battle of Lepanto in 1571, there were, about, 490 ships present TOTAL for both sides.

Compare that to the Battle of Artemisium in 480 BC where the Persian navy alone brought about 1200 ships.

However, numbers are not enough to decide a battle.

The Greeks only brought 271 ships to the Battle of Artemisium according to Holland, and they fought the Persians to a tactical stalemate and were wrecking them 4 to 1.

Improvements in sail, navigation, and seamanship, as well as advances in weaponry and other technology make a medieval navy more than a match for anything in the classical period.

However, and this is where it gets confusing, the fall of Rome led to the decentralization of a LOT of military power in Europe. Which means that there simply weren't as many organized navies in the middle ages. At least not the early part of it. However, by the so-called high middle ages the age of sail had truly begun and naval tech was off to the races.

Remember that by the end of the 15th century, Europe had begun exploring and exploiting the "New World".