But, have you think about that Dabura could maybe never have need to effort in his battles, and as well, that Freeza, Piccolo and Buu despite of exerting effort in many situations on a battle couldn't get stronger? What assures us that something similar happened with Dabura? Do we even know if Dabura has that great of a potential that if he trained (something unproven) he can get that much stronger?
The only thing that matters is that Future Dabura is shown being on Z Sword SSJ Trunks' level, so it doesn't matter how he got that way. It is what it is. You are using an argument from incredulity. Your incredulousness is irrelevant.
How about we never got to see Dabura using full effort against Gohan and he is doing it with Trunks?
It's never said Dabura wasn't using full effort. Your scan doesn't say anything like that.
Dabura was confident on fighting Gohan again and thinks it wouldn't be difficult to dispatch him.
As per your logic, there are other reasons why Dabura would be confident. For one, Gohan lost enough stamina during their fight where he had to take a sensu bean. In contrast, Dabura was sweating a bit but immediately caught his breath with no indication that his stamina had dropped by a large margin. Dabura's magic on top of Gohan's wasted movements would naturally cause Gohan to lose more stamina which would result in him losing the match even if his power was slightly greater than Dabura's.
Gohan was rusty so he would be outmatched by someone like Dabura who has his skills sharp, not to mention his magic. The manga is enough for this.
His magic didn't served to that purpose initially, he wasn't even able to injure him, let alone kill him, in this scene he is completely confident on killing him. This is without saying that his saliva didn't also as he quitted his glove and Gohan was also able to destroy his sword.
That still isn't enough to say that Dabura had more power that wasn't shown prior. That's a pretty subjective point.
Ah yes, then Dabura thinks of defeating Gohan, even though, he couldn't prior and wanted Vegeta to do the things for him, but now he is fully confident as he is and doesn't think much of Gohan.
Couldn't there be another reason for that?
Don't know. You tell me.
Dabura suggested Vegeta be made a Majin out of convenience. Vegeta loudly proclaimed he wanted to fight Goku and Dabura took the bait to have the Earthlings fight each other for them.
Dabura knew that Vegeta would be the best fighter and had already discovered that Vegeta had maliciousness on his side who can be manipulated by Babidi, as well as they can use him to revive Buu.
Does Dabura call Vegeta the best fighter? I recall he calls Vegeta a splendid fighter.
My bad, Dabura called Vegeta the perfect fighter:
Dabura is pretty arrogant and considered himself the strongest in the universe, heck, he even had no problem fighting all the three saiyans at once, do you think he is going to use all of his effort against the weakest of the three? If one was better was him, as Gohan needed to eat a senzu after their fight, while Dabura was fresh. Dabura not holding back against Gohan my ovaries:
Unfortunately we don't really get any statements indicating Dabura was putting in more effort when later ambushing Boo or that he raised his power (manga-wise).
It was in my previous post. One reason would be that Gohan's stamina was lower and was making wasted movements. So while they were initially on par with each other, the gap widened when Gohan's stamina was falling faster than Dabura's.
