Nah, you're right about Ki control but what happened with 17 isn't like the Krillin fight where Goku clearly just went SSB to test him and see if he would bytch out when he seen god level opponents in the tournament. The Krillin shyt wasn't even really a fight, he just threw some Destructo disks at base Goku, then hid the second Goku turned SS until Goku walked into a hole that Krillin made with a hidden Destrocto disk. When Goku went SSB, Krillin just stood there shook, shytting himself until he was like "fukk it, I can't let my daughter see me going out like a bytch
" then he proceeded to almost get vaporized by SSB Goku's Kamehameha. To remove any doubt, they had Goku ask Krillin "So what'll you do now
" when he went SSB to make it clear what his intentions were.
In the 17 fight, 17 beat the shyt out of SS Goku effortlessly until Goku was like "oh shyt I better go blue
". Then instead of being in awe of SSB like damn near everyone else that has seen the form for the 1st time, 17 just casually commented like
"oh u can turn into that color too huh
" then blocked Goku's SSB kamehameha like it wasn't shyt and proceeded to smack SSB Goku around the skies. On top of that, in case there was any doubt of how strong he was, they had 17 mention that he was holding back the whole time. They were clearly trying to imply that 17 is SSB Goku level at the very least