Gokuden wrote:
When Trunks was going all-out with Cell, his power did not fade, it rose, until a certain point where the only thing holding him back was his lack of speed. His reservoir of ki was steady.
Trunks never used a ki blast against Cell that used up such a large amount of his ki, let alone doing so after fighting an opponent both stronger and faster than he was during the majority of their fight. If Goku hadn't used the Shunkan Idou Kamehameha when he did, or used so much ki when he did, then he wouldn't have wore himself down so quickly.
Gokuden wrote:
When Trunks said Gohan's doing it properly, he wasn't referring to raw strength, quantity of ki, or fighting technique, oh no, it was SPEED.
When Goku blasted Cell to near-death, then gave him a sensu bean as a gesture of goodwill, or because of his mild retardation, he said he would have killed Cell had the blast been larger (same applies to Super Vegeta). But, Cell did get a Zenkai boost, how big it was is a mystery, but since Saiyans at near-death get a massive boost, you can expect the same from someone with the same infrastructure.
I don't recall Goku ever saying that his blast would have defeated Cell if it had been larger, and the whole line of Trunks saying Gohan was doing it properly wasn't in the original manga, just a dub line as others have pointed out. Likewise, there's no mention whatsoever of him receiving a zenkai as a result of it. The only zenkai ever stated or inferred to happen after Goku's time in the healing chamber during the Freeza Saga was Cell's zenkai following his self-destruct attempt. Since no other zenkai is ever suggested, nor is Cell's strength ever mentioned to increase as a result of that particular recovery, we can't assume there was one.
Gokuden wrote:
Had Trunks been fast enough, he would have ended the Saga before the Cell Games as a humble half-breed warrior.
Cell wasn't using anywhere near his full strength when he fought Trunks though, so any suggestion that Trunks was stronger than him is only in reference to that suppressed level of power. Furthermore, when Goku is getting ready to announce who would be replacing him, Cell even says that while he suspects that Vegeta and Trunks had both become stronger since their last fight, he's certain that they hadn't reached a level to surpass Goku, meaning that if he didn't believe Trunks was stronger than Goku now, he definitely knows Ssj Grade 3 Trunks was weaker than him before hand.