dragon king

Hello! everyone. There's something that has been on my mind for very long and I want to share it now. As per the other Dragons and our own experience, Igneel when at his full, orginal strength could have defeated Acnologia, still he DIDN'T defeat Acnologia 400 years ago when he was at full...

It is say in the manga that the dragons only have a fraction of their original power (that is why they hide on the dragon slayer's body) but still Igneel manage to fight 1-1 with acnologia and he even cut his arm... In normal conditions would Igneel beat Acnologia?

Who or what do you think is Acnologia exactly? What power does e had before turning into a dragon? What is his connection to Zere and thereforeto IGneel and maybe even Natsu? Maybe Zeref knows Natsu, because he is just a part (the ''good half'' of Acnologia himself and Zeref separated the two as...

Can someone enlighten me about my question? How Strong is Igneel? He doesn't look that fire type of a dragon to me but atlas looks like a good fire dragon but how come he is weaker than Igneel?