Law said:
Cell did have it. He told Goku to take a senzu to get his power back and that would make the fight "a little more interesting". Based on how warn out Cell was when he told this to Goku, he would be well below FP SSJ Goku, yet he was still going to win easily if Goku got back to full power. He still had all of his power in his reserves that he could bring out in an instance.
If Freeza was not at full power, why would he be announcing each passing 5% that he was at when he was powering up? Would he really do mental math on the spot and know he was at 85% of his 30% power? Seems illogical.
Cell didn't have it either. What you're arguing is that Freezer was NOT affected by the injuries in terms of losing power, but that's clearly not the case with Cell, who had to eat a senzu to recover the strength he had lost, which is directly contradicted by Goku when he states that Cell's Ki had decreased after the KameHame.
Now, regarding what Cell says about Goku, there are multiple explanations to that:
1. Cell was considerably stronger than Goku. At least, he was a good 20% above, so it's possible that his reserves were still high enough to compensate for the strength lost in the fight (he wasn't badly injured like Freezer was, and yes, the KameHame that blew his head should've killed him and even Toriyama admitted that, but in the manga it wasn't treated as a severe injury nor anything that could decide the outcome of the fight).
2. Cell was overly confident, and if Goku had eaten the senzu he would've lost (like when he was convinced he would surpass SSJ2 Gohan but he got trashed instead).
