Goku is completely shocked at how Raditz handled the Kamehameha. He gasps at the feat and even says, "What kind of guy is this?"
To me it seems clear, Goku expected the Kamehameha to do at least something, or for Raditz to have to full on block it or something, he doesn't seem to indicate previously that he ever thought he could win with it, always talking about going after the tail or something, but yeah, I think Kamehameha should be rivalving Initial Raditz and Powered Up Raditz...
And, as far as I'm concerned, Raditz has to use his full strength to fend it off the way he does... No need for him to be playing games with a suppressed power if the blast is giving him this much difficulty...
Raditz shows his power against the Kamehameha, and shows off this power levels speed against the SBC...