This actually isn't true, the same item got converted at the same rate for everyone, taking into consideration tier and level.Everybody is aware that different players received different compensation for the same items.
The only "exception" you may notice is whether the item was equipped during the migration or was in the inventory and a regiment had a lower level item of that type equipped.
Case A (equipped): The item got converted to an equivalent of the new system. Obviously for everyone with the exact same criteria. All mythical items level 13 have been converted into mythical items level 49 to give a numeric example.
Case B (inventory): The player received enough resources to upgrade the equipped item to an equivalent of case A.
The outcome is exactly the same in terms of final item obtainable, either you have let's say (Case A) a legendary weapon level 32 or (Case B) a common weapon level 3 and enough resources to upgrade it until tier legendary and level 32 (that is the same of Case A).
A valid criticism that has been moved is that having the resources instead of the fixed item allows you to in fact decide on upgrading a different item, that is true, but this does not mean that the same item has been converted for different values for different players. In terms of raw values (gold, ingots and cores) the conversion is perfectly matching.
That said, in case you are aware of a clear situation when two players got a different amount of resources for the same item, that not intended behaviour and can be considered as a bug. Please reach us out via support (you can find a quick path in the game settings) providing the IDs (or PvP names) of the two affected players so that our development team can compare what they received and take proper actions if the situation requires so.
I hope my explanation was clear enough, I'm now looking forward to receiving a support ticket from you with the aforementioned details so that our developers will be able to investigate.