Not a particularly good assumption to make imo.

For example, we now have multiple solid lines of evidence that ancient Polynesians were making it all the way from Oceana to Peru, and back, with some degree of regularity. We see this in human genetics on both sides, as well as the introduction of the potato to Oceana. The Polynesians had a very different approach to navigation than europeans, one based on amassing a great deal of knowledge about currents, bird and sea life behavior, as well as intuitive celestial navigation.

It seems likely the first folks to make this trip were forced into it via a storm or such, but what's stunning is it's clear some of them were able to map the path well enough to be able to find their way back home later. There are still some people who use these navigation skills today. Look up the maps they make with sticks and twine. They're pretty interesting.

In any case, my point is there's historically been a lot of variation in sailing techniques and technology. If you looked at an ancient Polynesian proa, you'd almost certainly assume it's impossible they could cross such a vast distance. But they did. No doubt many drowned, but we know as an empirical fact some made it, and made it back.

The ancient Phoenicians were brilliant mariners. They invented the trireme, the keel, the amphora, etc. It's easy to think of these as crude technologies, especially based on hollywood portrays, but the reality is these were the NASA astronauts of their era. Coordinating large number of rowers that are stuck in the hull and blind to their surroundings is not as trivial as it might seem.

As another comment points out, triremes and similar vessels usually beach at night. The sailors are capable of dragging the things considerably away from the water line. In fact they have to do so relatively often to let the boats dry out for some number of days. Likewise we know of several places around the med where ships were dragged considerable distances over standardized portage/ferrying routes routinely.

This is very different from the ships the Portuguese were using in the 1400s. Their ships were bigger, with deeper draft, and with rock ballast in the lowest hold for stability. They'd have a limited capability to use poles/oars to push themselves through shallows where they were partially dragging, but covering longer distances on land with such ships is infeasible without far more people. Combine that with an aversion to sailing out of sight of the coastline, and you can see why they'd face more issues in this area.

In any case, I'm no authority on these topics, just another curious person on the internet, but I find it entirely plausible the Phoenicians simply walked their boats past this obstacle.

Modern humans have an unfortunate habit of projecting our own perspective on labor onto ancient peoples. Humans are capable of truly astounding things with nothing more than their bodies when focused on a common goal for a sustained time. The best example is neolithic architecture. There was no magic trick to building Stonehenge. They just used a ton of people over a long time to drag the rocks there, and then sea saw them into position.