My guess is that there's no clear market rate for any position. Companies can always say there's a wide range between lowest and highest paid for any given role.
You posting that link over and over doesn’t obviate the fact that we look around collectively and see H1Bs getting paid at the bottom of the band.
H1B holders will get paid less over time due to not being able to leave companies at the drop of a hat. A similar but less significant effect holds for TN visas. I have not once seen any significant pay discrepancy for two comparable software engineers at the same company based on visa status.
I don't believe this for a second.
Were they outsourced?
Visa holder wages are publicly available. People in this thread are making stuff up to support their views.