The Mandalorian Season 2

[Fyraltari]

A.) Regardless, Luke said it so it exists and I can try to justify it.
2.) It wasn't really oversized; there are generally two types of Stormtrooper armor in ANH, Hero and Stunt*. The Hero suits were made for the heroes - Mark Hamill and Harrison Ford. They were sized for those people in mind. That being said, the helmets are bigger than you would expect when you hold them.
iii.) IRL, no, Hamill called it. You can't see a thing in those helmets. Especially if they fog up, which happens all the time. Fun fact, 501st events will nearly always have handlers.

Right, so the helmet aren't oversized but foggy in real life.

In universe though, Luke is called out as being shorter than the average stormtrooper and wearing an uniform not designed with him in mind. So it's likely he can't see jack becaue the helmet isn't a good fit.

*Don't ask me the differences. I've read it all and even I can't tell you.

The hero suits were made for the actors playing the heroes to wear while the stunt suits were made for the stuntmen playing the bad guys to wear?