Yes - a giant striding up out of the sea! The constellation of Orion must have been important because of its reappearance in winter, because of its dramatic shape and because it is easy to recognise. Whichever way people interpret and make shapes of star patterns - Orion is big and in-your-face. Orion and the Plough are probably the only star patterns that most modern people can identify

The story of the blinding and healing by Helios and love of Eos is the Greek view. Putting aside the Egyptian pyramid line up and Orion's belt pattern - it does seem that he was of significance to them also.

But what would be really interesting is a northern legend that links a giant from the east appearing at the commencement of winter. That would support your suggestion that some stones align to the appearance of Orion rather than the equinox.