You're right, Goku couldn't sense Dabra's ki--but based on how Dabra moved when he attacked them outside Babidi's ship, Goku estimated that he was ~ Cell... And we were ultimately given no reason to doubt his assessment.
It's also worth noting that Goku stated Dabra was tougher than he first thought, after seeing him use magic against Gohan: (please log in to view the image)
So I'd say Dabra was Perfect Cell-level, at the very least--possibly a bit stronger when you factor in his magical abilities.
__________________
"I am tired of Earth. These people.
I am tired of being caught in the tangle of their lives."
All that scene indicates is that Dabra might be slightly more powerful than Perfect Cell, with his magical abilities factored in... Still well below Cell Games SSJ2 Gohan, though.
__________________
"I am tired of Earth. These people.
I am tired of being caught in the tangle of their lives."
Makes sense, since SSJ2 Gohan was well above base Perfect Cell level, to the point of toying with him rather then finishing it quick.
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Never let anyone else define you. Don't be a jerk just to be a jerk, but if you are expressing your true inner feelings and beliefs, or at least trying to express that inner child, and everyone gets pissed off about it, never NEVER apologize for it. Let them think what they want, let them define you in their narrow little minds while they suppress every last piece of them just to keep a friend that never liked them for themselves in the first place.