I have a 2017 WRX and it says it came with the STI short throw package. I'm not really sure how to tell if it actually did because I haven't driven one that didn't. Also if I was looking for an aftermarket short throw shifter would I need to look for one for an STI being that I have that package or just look for one for the regular WRX?
The shifting mechanisms between the WRX and STI models are completely different designs. The term "STI Shifter" is a formality only -- it's not actually related to the model.
Correct me if I am wrong, the STi STS from the factory is the linkage and stuff that is replaced. Not actually the height of the shifter itself. You should be able to purchase a kit from kartboy that includes a shorter shifter as well as the stiffer bushings. Having those along with the linkage shifter kit from Subaru will give you basically the best STS you can buy.
When I bought my '17 Limited, it did not have the STI STS installed, but the dealer threw it in as part of the deal. A few days later, they replaced the entire shifter mechanism, and gave me the old stock one. This is the shift lever and the mechanism that bolts to the floor. They did not change the cables, or levers/bushings (i.e. the things that Kartboy or Perrin replace in their short throw lever kit).
The STI STS is shorter in throw than the stock part but it has the same shift lever length, so the shift knob is still the same height from the floor. The shift throws are shorter but the feel/effort is about the same.
Changing the bushings is going to make a lot bigger difference than swapping from the STI STS to an aftermarket STS, IMO. I had a kartboy on my old WRX and the STI STS on my STi, and the throws are very similar. The bushings, however, made a world of difference in the feel of the shifter.