Cripes - how about a little fact finding before posting inaccurate WW2 historical details???
Russia had its share of WW2 aces - the highest scoring ace being Ivan Kozhedub with 62 kills. More impressive is Russia's number 2 ace who flew P-39s - an aircraft rejected by the Western nations for the air-to-air combat role.
Russia's highest decorated Air Force unit was an all-female regiment. The "Night-Witches" were assigned outdated Po-2 (cropduster) bi-planes in which to do battle. A record 18 (bombing) missions a day were once carried out - war survivors logged over 1000 combat sorties each. 23,000 total bombing missions, 38 air-to-air combat kills, and only 31 losses. Not bad for a cropduster.
Notwithstanding, Russian pilot training and tactics were wholly inadequate for the first half of the war. This allowed most of the high scoring German aces to achieve extremely high kill ratios on the Eastern Front as compared to the Western Front. Then came the later half of the war...
Late model Russian aircraft on the other hand, were on "generally" on par with the German Me-109F/G and FW-190A planes - many were inferior but others were considered superior. Late model Lavochkin and Yakolev fighters, and Pe-2 and IL-2 ground attack bombers were all excellent planes. Recall that the Luftwaffe had ordered a directive in late 1944 for its pilots to avoid combat under 5000 metres on (Yak-3) aircraft lacking an oil cooler under the nose - the Yak-3 was an outstanding dogfighter and is considered by many historians to be a top 10 fighter of the war.
I digress - this is afterall a WW1 forum.
I too find the Fokker DR.1 lacking in the game - much like the SPAD, but in a different way. I'll take a Pfalz III anyday instead. While the DR.1 had a good (initial) climb rate, it also dove poorly. If you modify the DR.1 climb rules I would argue that you would likewise have to boost the dive rules for the Camel, SE5A and SPAD. I would also disallow the DR.1 invulnerability rule you propose if I played in your campaign. Recommend that you play with the altitude rules; it won't make a huge difference but it will provide a small boost to the DR.1 (and also to the SPAD). Further consider that if you are playing a historical campaign of sorts, the axis player should be fielding about 20 Albatross fighters for every Fokker Triplane in the game.
I don't think that the DR.1 made a big impact on the war as it only flew a few months in service from late 1917 to early 1918. The 320 that were built suffered from mechanical and design flaws. IMO its fame surpassed its notoriety. Arguably, its greatest contribution was that its failures led to development of the Fokker DVII.