The video doesn't provide any explanation for the three hypotheses, so I can't agree nor disagree, what I can do is try to give an explanation.
About the sky it depends on the composition, blue is probably one of the most common colors in atmopheres (see earth, saturn, neptune) so yeah it might be.
About the oceans, if gravity is higher than Earth probably terrain is a bit flatter too, but it purely depends on the quantity of water on the surface, so it's impossible to say if it's a common feature or not. The color... yeah, water in high quantities is blue so if oceans are made of water and the atmosphere is blue, oceans can't be any color but blue/turquoise. This might be a quite common feature.
About the vegetation, I have no idea why an hypothetical earth-like vegetation should be purple. Is not a color of the black body spectrum, so plants would have no benefits reflecting it. Also "purple" doesn't have higher wave frequency than blue as we might think (because it's ultraviolet radiation) but it's just the fusion between blue (it have been also called violet) and red. On earth there are very few plants which are purple, and they're mostly flowers, so, as long as there are not biological processes that we don't know, it's very unlikely that natural selection would select purple plants rather than any other color. If the parent star was a bit dimmer than the Sun, that is the case for superhabitable planets, and assuming these plants gain energy using the light coming from their star, the most likely color would be red/orange, which is the peak of color in the spectrum emitted by K stars and because they would get less light from the sky, so they need to keep the nutrients and protect the leaf from falling prematurely.
The universe is not required to be in perfect harmony with human ambition.
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