I agree with
Escanors Pride. The fight was a combination of both physical and mental performance. Gray and Lyon are
at least on Ur's level (Low-Wizard Saint Tier) individually. Lyon was obviously impacted psychologically so the main purpose for this fight was for Gray to help him overcome his emotions, which he had already done himself. This is seen in the following panels.
In a way, Hiro Mashima portrayed the difficulty of this fight the same as every other character who went against their Historia. It really just depends on how you define the difficulty of the fight.
But it should be consistent for all the fights. Meaning if you rate Gray + Lyon's fight a certain difficulty, it should be the same with Erza + Wendy + Juvia + Meredy + Laxus. There are subtle differences that I will explain though.
In my opinion, they were all able to defeat the Pre-Timeskip characters quite easily. The fact that it only took
one combined spell to take down Ur, I would place the difficulty of this fight at
Low-Difficulty. It is true they took some damage but that was mainly to show Lyon overcoming his emotions. Gray was restricted because of Lyon. Similarly, Jellal was restricted because of Kagura.
Laxus, Erza, and Wendy seemingly defeated their opponents pretty easily
despite being injured beforehand.
But they didn't have any emotional attachment with their Historias, so that would change the dynamics of the two situations immensely.
How about Meredy and Juvia?
I would say their situation is the most similar to Gray and Lyon. Again, I rate this a
Low-Difficulty fight. Note that they have the same amount of scratches as Gray + Lyon. So are there any differences? Yes. Neither of them had attachments to their Historia. Meredy and Juvia struggled because they
aren't as strong as Gray + Lyon. Gray and Lyon struggled because they
have emotional attachments to their Historia while Meredy + Juvia didn't.
So to sum up the power ranking. Lyon has no other power-ups and since Gray convinced him to go all out against Ur (to surpass her), whatever he displayed here is a good indication of where he is which is around Pre-Timeskip Ur's level (Not something to underestimate). Gray, on the other hand, wasn't using full power and he didn't even use DeS mode so that would place him well above Erza (Jura's Level or Mid-Tier Wizard Saint).