You could say the same thing about the original Zelda and Zelda 2: The Adventures of Link.
You could say some of the same things about Zelda, but not all of the same things. For me what makes Metroid unplayable is the combination of the factors I mentioned.
You could argue that Zelda also suffers from the lack of visual cues and that this requires the player to bomb/burn random points on the map. The difference between Zelda and Metroid, however, is that Zelda's areas are visually distinctive and the different sections of the map actually fit together unlike in Metroid where they are just separated by doors. In Zelda this gives the illusion that there is connective tissue between the different screens and it allows the player to make a mental map of the different areas much more easily.
Zelda also deals with health in a much more efficient manner. It has Fairy Fountains at specific points throughout the map and it also gives you the option to buy red potion. Unlike Metroid which as far as I can tell always requires you to farm enemies for health.
Zelda also plays better in my opinion. As I said in my previous post I find the way Samus controls in the original Metroid to be squirrelly and imprecise (particularly as far as platforming goes) and shooting enemies just doesn't feel satisfying. On the other hand controlling Link with the D-Pad is perfect.
I'm not trying to s*** on anyone who likes the original Metroid. I know there are quite a few people who adore that game. It was an ambitious game and one which I admire to a certain extent. Without the original Metroid we would not have got Super Metroid, my favourite game of all time. For me though, the original Metroid, ambitious as it was, is fundamentally broken and I really do find it unplayable.
*I can't speak to Zelda II because I haven't spent more than 5 minutes with it.