no, no it isn't impressive.
Not impressive compared with the names BJ's faced, but wins over Parisyan, Florian, Guida, Diaz and Stevenson are impressive victories, and contribute to a record that's certainly stronger than BJ's was before he got his first title shot; and a stronger resumé I believe than the one that Florian and Stevenson had before they got their title shots. I struggle to see how a 23-2 record isn't impressive, it's not like he's been fighting all can's in the UFC.
I'm not saying Sanchez will beat Penn, I don't believe he will, but I think he's getting pretty harshly criticised on here. I think he's a talented fighter that's going to push BJ Penn hard, challenge him in the stand-up and challenge him on the ground. This isn't going to be an easy fight for BJ Penn.