We don't really know about Dabura. Yamu and Spopovitch get deformed something fierce during the Majin control, and Majin Vegeta also seemed a little out of control at points. But Dabura is at all times pretty relaxed and chill. Maybe since he is supposed to be evil already the control went easier on him and just didn't give him that much of a power up. Remember that a big thing that the Majin possession did to Vegeta was to get him back to his unbridled evil form of thinking.
We don't really know how much more powerful it made Vegeta, but it clearly doesn't fill the gap between Cell saga Gohan (which regular Vegeta had achieved by Buu) and SSJ3 (which neither Vegeta nor Majin Vegeta never even approached), so the powerup wasn't THAT big.
Assuming a similar powerup for Dabura, which seems to be on Cell level while Majin, regular unpossesed Dabura could still be beyond Trunks' reach.
Yamu had perfect control over his actions, Spopovitch was just sadistic. They pushed their bodies to the extreme and got those results. There are two reasons, 1) their human bodies were not initially trained to use this kind of power 2) Babidi sees them as pawn and doesn't mind if they overdo it.
2) Vegeta was not evil at all, he was lying to get his fight, Goku called him out and he was right 100%, Vegeta admitted it himself.
3) Vegeta went through the whole ordeal of getting the majin boost, to get something you think is marginal... Yeah no.
SSJ3 doesn't count because it's a useless form that can't be used by normal living beings.
Both Goku and Vegeta were at the maximum power of ssj2, after Vegeta turns majin.
Vegeta got really hurt Goku passed him, and he said he accepted babidi's deal because he saw how much Spopovitch improved with it.
Why would Dabra accept to be a puppet, if not to get much more power ? He was a devil KING, now a puppet, for the simple sake of getting more raw power.
You can't really spin it the way you want. Like sure we don't have facts to argue with, but it's hard to believe Dabra was on Cell's level without the boost.
And as for Trunks, zenkai boost from his death + years of training after witnessing Gohan's power. Still a lot for you to say Trunks might be leagues behind Dabra...
Huh? Isn't SS Blue = god ki + SSJ? Doesn't the possession of god ki make someone a god?
I don't know if that was from the FNF movie.
But not that's not true at all in Super. SSJB is a better controlled ki, but drains more stamina. They are not gods.
And Goku has never showed any of his god abilities ever again, after losing the god form. (dragon thingy, ki absorption, regeneration etc..)