WetWired, the one major flaw in your argument is your statement that these things are "hardly series defining". The fact is, Super Metroid was series defining, despite your opinion on its quality.

Has the rest of the series made use of the map system crafted by Super Metroid? Yes. Has the rest of the series employed the use of just about all of the equipment invented by the game (including the ones you don't think are worth the time)? Yes. Has the rest of the series used Super Metroid as the foundation for its design and atmosphere. Unquestionably, yes.

Your opinion on the quality or importance of Super Metroid's offerings to the series is irrelevant. It doesn't matter that you are of the opinion that Metroid II is a better game, or that I prefer Metroid Prime over Super Metroid. The quality is not the question here. The fact that Super Metroid created the vast majority of the staple elements of the series (good or bad) makes it the defining game in the series.