The power of a character was basically whatever he felt like at that time. His normal abilities were increased when used his ki to enhance them, that's why going Super Saiyan boosted his power, it multiples his ki. Otherwise he is not that tough.
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I've read the wikia enough to understand how their power works fam. What I'm saying is, regardless, he shouldn't have fallen to the ray gun. He either should've been quick enough to block/dodge it even in a powered down state, or strong enough to just take it without blinking. Even at rest, Super Saiyan Blue should've been giving him a power multiplier of well over 400x. It's just one of the many loopholes present throughout Dragon Ball Z and is inconsequential.
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But at rest he is not using his power to enhance his durability. But yes it is irrelevant to the discussion.