It's not like the DBZ fighters had protection against energy drain, anyway. IIRC, the cyborgs 19 and 20 and that weird thing in the Buu saga drained energy just fine from the DBZ guys. Though the cyborgs drained too slowly against the stronger ones and the weird thing can't control it's intake (lol Goku's way of killing that thing)
Nagato doesn't need to touch Goku, all she needs to do is rewrite the universe, and when it happens, it happens instantly, and Nagato can handle the power.
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My Little Phineas and Ferb: Summer is Magic!