Also in regards to Gohan vs Cell, Gohan even thought Cell was holding back, not just Goku. Which should be direct admission that the Ki level Cell used against Goku was far surpassed by Gohan, even if Cell was holding back his speed.
Chapter: 402 (DBZ 208), P6.5, P7.1-6
Context: after Goku asks Gohan to be the next one to fight Cell
Piccolo: “Don’t talk crazy, Goku! There’s no way he’d be able to fight! It’s true that he’s raised his abilities so much that he’s unrecognizable, but his opponent is Cell, who even you were no match for!”
Goku: “Piccolo, Gohan has more unbelievable power than we think. Think about it. He’s fought the same as everyone since he was a little squirt…When I was about his age, I wasn’t anything special.”
Kuririn: “B-but even if he’s become a Super Saiyan…Th-this is so quick…”
Goku: “In the Room of Spirit and Time, the dormant power sealed away deep, deep inside him began to be released. Why don’t we try asking him? How about it, Gohan? Did you think that dad and Cell’s fight just now was too incredible and you couldn’t keep up?”
Gohan: “N-no, I didn’t think so…But neither of you were fighting all-out, right…!?”
Goku: “I don’t know about Cell, but I was going all-out. So in other words, to you it felt like I was holding back?”
So we have this:
Goku < Cell (withheld speed) </< Cell vs Goku/Gohan (ki level) </< Gohan
So we are once again left with the question as to how Cell suddenly became a threat to Gohan if he didn't level up further.