Personally, while I defer to others on the historical modelling of the DR.I, I think balance-wise the main problem with the DR.I is the completely one dimensional game-play that centers, and is limited to, exactly the DR.I’s most advantageous envelope. The one mission profile available is exactly where the DR. I excels. So with-in that context, it will enjoy an unbalancing advantage.
Start adding other mission profiles (e.g. 15k Gotha bomber runs to destroy field and strategic resources, Fast moving SPAD XIII attacks on observation balloons, Zeplins at 20k, etc) and you would start to provide other contexts in which the DR.I might not dominate. It will still dominate its part of the arena ecosystem, but there will be other areas and mission available where the DR.I might not be the best plane to choose. That will start to add variety.
As long as there is only one mission profile available, and it’s the one dogfight available on the map, between the only 2 fields that get used, between the same 2 countries, and at the same alt it always is, then it will remain a mostly DR.I arena, most of the time (when anyone is actually in there).
Regards,
Wab