I think you have to try at least 6-10+ examples of a particular varietal of yancha before you may start to notice some common characteristics of the type. The fact that some teas are sold under the wrong name makes this task even worse.
I believe that processing trumps varietal - that's not to say that the various sub-varietals don't have specific characteristics, but depending on the way the tea is processed (level of oxidation, type and level of roast, how long the maker waited after initial processing, etc.), how / where it's grown, when it's harvested, etc, the tea will taste very different. Someone with a lot of experience might still be able to tell by the taste, or even by the size / shape of the leaves, what type of tea it is, but I think you could fool most people, myself included, with the processing.
I'd even go a step further, and say that with yancha, it's not worth preferring a specific varietal. I would rather have a great tea, a maker's or vendor's best tea, of some unknown or obscure varietal, than a mediocre tea of a more famous variety.
There are, of course, some trends in the way specific teas are made or the taste that you'd expect. But I would not at all assume that you were sold the wrong tea. Just keep trying different teas. Also, you can experiment with trying to bring out the best in the LCSX you purchased recently. If you try it different ways and still can't get a good result, it's possible that it's just not very good.
I have tried a few of 7 Cups teas, and while they're not really to my taste, I will say that they tend to be unique. If this is the taste you like, I'd keep buying it from them, because I'm not sure how much luck you'll have finding something similar.
As you might expect from the name, shuixian's characteristic taste is supposed to be pretty floral. Some examples of the genre will bring this out more than others.