According to this site, my company has LCAs with salary 12% to 26% MORE than what I'm making for the same title! I didn't know I was getting screwed like this. I was happy with my job until I saw this site today.

I'm not sure what to do now. Should I tell my boss about this and ask for a big raise this year? How would they react if I showed this data to them and demanded that my salary at least match these numbers?

Sorry for that. I don't think anyone can predict how your boss would react to such demand.

That said, it might be that those colleagues making more than you do simply offer more value to the company, or were better negotiators when discussing their job offers.