Nothing suggests his ability to detect powers below him are compromised though. What he cannot do is judge the powers so much higher than he anticipated. He does not realize just how much more superior the Super Saiyans actually are. But he should be able to tell that Suppressed Piccolo ~ Humans in my opinion. But you are right, it doesn't have to be taken as gospel.
Haha BPP, my idea of "realm" here, is taken a page from the Freeza Saga. Compare the Base Saiyans to everyone else, clearly they are on astronomically different levels. But if you are 10-15% of a Base Saiyan at these elite levels, it's impressive no?
Let's try numbers here....
Base Vegeta 100
Base Goku 95
Base Trunks 90
Base Piccolo 80
Gohan 40
Tien 30
Krillen 25
As you can see, this is still somewhat in the realm of a BASE FUCKING SAIYAN. Krillen being 25% of Base Fucking Vegeta is insane. That is highly respectable wouldn't you agree?
Also, let's not forget that these are new and improved Base Saiyans. Base Saiyan Goku/Vegeta on Namek would not be Gods to this crew me thinks.
So that's why I think Namek Base Saiyan level is where the Humans top out. And that level is ultra impressive.