He's sensed powered levels before even seeing them many times in show. I'm pretty sure the androids in dbz were sensed out because of their power levels as well and they're robots.
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But they're not even remotely the same as the Vex. I really doubt they'd even register in the same way.
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Whatever you say.
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DBZ's androids are advanced almost to the degree of biotechnology, and possess the ability to channel the same power Goku and others do to produce their energy-blasts and whatnot. Vex? They're metal frames with weird, prokaryotic sludge in them. Their weapons do not POSSESS power, they draw it from somewhere else entirely. So why exactly WOULD the Vex rate on Goku's power-scale? The only ones I can see showing up for him are the Minotaurs, as they possess energy-shielding, the Templar, and Atheon.
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I'm just gonna end it by saying there are way too many variables involved.