If Haki = DS Magic then an argument can be made for Loki winning otherwise Loki wouldn't have the means to put Acnologia down
I think DS magic is needed since Dragons has insane durability, you can´t hurt them.
As example to bypass that durability you need DS otherwise you can´t hurt a Dragon scale...
Same happend with One Piece too.
Unless you pose adv CoA/Adv CoC you can´t hurt Kaido.
Either you bypass that durability with hax abilities or you wont hurt him.
Goku don´t have any magic, but no one would doubt that he can one shot Acnologia.
Dragon vs Dragon as example, both should be able to hurt themselve.
And given you can even kill immortal beeings with adv CoC, Acnologia wont survive lot of attacks.
Fairy tail is more hax(better than One Piece), but when it come to raw DC/AP power, they are below One Piece.
As example, do you think Loki is below Igneel as example? I doubt it, if Igneel can manage to cut off Acno hand, just imagine the island size Loki.
Acnologia is pretty strong, no doubt about it, but there are levels and I only see Space/time powered up Acno to be able to defeat Loki if he can control that form(which isn´t the case).
As example this was Igneel strongest breath attack:
vs Loki Breath attack:
There are levels to this..
Loki breath is not just a lightning element attack, it is fused with Adv CoC...
Igneel fire breath was strong but not even close to the power/size what Loki show off...
I think when it come to raw power, Loki dragon is one step over Acnologia meanwhile when it come to hax Acno is better(space/time power) but he can´t control it proper.