He was in DF and there were hints of PoF since talks of defending his friends were happening. Gajeel didn't hurt Aldoron at all. Aldoron was not taking him seriously in fact we know once Aldoron did get serious with the thicket of arms, Gajeel was impaled immediately and would've been killed had it not been for Brandish.
Aldoron as a God Seed at full power killed Natsu with ease and the latter couldn't even see his attacks. So for you to say low-diff is lowballing quite a bit because he himself said all the power that comes with that size is in him.
It's not all about MP, Acnolgia as far as I could tell is way faster than Aldoron, he moved so fast that God Serena took a few seconds to realize that he was dead and August didn't even see him after he dashed towards Serena. As far as I could tell Acno could outspeed Aldoron rather casually, which is bad because he seems to be more of a long-range fighter rather than a CQC fighter, so if he wanted Acno could easily close the gap and make it a CQC fight. As far as I remember Aldoron has shown zero speed feats unlike Acno.
Acnologia's spells seem to be far more destructive than Aldoron's, plus he has more variety, considering he's the Sorcery Dragon Slayer it's safe to say he knows his fair share of Magic, which again, is a threat to Aldoron and a point against him.
He could straight up eat whatever Aldoron throws at him as he can literally eat anything to replenish his magic.
It's safe to say he is far more durable than Natsu, so Aldoron's bark attacks shouldn't hurt him as bad as it hurt Natsu.
Acnologia is better at long-ranged attacks since his seems to be stronger and he has spells that he can do at a range.
His main human attack (what he does to Serena and the Dragons in flashbacks) should do quite a bit of damage to Aldoron while I don't see Aldoron doing much damage to Acno. (Note, I'm not saying he could nearly rip Aldoron in half with that one hit, I'm saying it should do some pretty heavy damage if he can land it)
Lastly, as the Dragon of all Sorcery, he's pretty much immune to any attack if we don't go by POF, so Aldoron can't really damage him with Magic without a friendship boost.
I'll give Aldoron the benefit of the doubt and say that he could push Acnologia to a mid diff fight.