DBZ is kind of a dumb anime like that. There aren't any feats you could actually judge their strength by because they only went all out against each other and Toriyama kept getting his own power scaling wrong. Vegeta was a planet buster at a power level of 18,000, and then Frieza's first form was at 450,000 or something ridiculous. After a few strength increases by multiples throughout the series we get to the Buu saga where apparrently they only have enough strength to destroy the earth 10 times. For such a popular show it was extremely sloppily done. I thought it was because his guard was down. He was still Super Saiyan Blue. Either way, he shouldn't have even been fazed by it.

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.

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.