Don't forget about the acceleration abilitys of these WWI aircraft...... just because a plane may be 30 or 40 mph faster "at top speed"......means only that..it is faster at top speed.....
while dogfighting in these WWI era planes, once one wants to disengage and extend, gaining acceleration is going to take a bit of time ( time here is thought of in seconds )...... so you are in the D.VII. and you are wanting to break off and extend from a Dr1..... well that DR1 is a heck of a turner, and gets around the turn circle quiet quickly, and will be able to continue pinging you while you are accelerating to get out of guns range......
now if you are diving away to extend you will gain a little bit more quickly, but it still is gonna take a few seconds to be able to pull out of guns range of the DR1 until your D.VII reaches its top speed
edit: and I totally agree with FLS's statement about in Real Life these battles of the 2 planes took place at significant higher altitudes, verses the on the deck fights or under 3K or 4K alt fights we see in the WWI Era Arena...... so the fights in the WWI arena need to be compared to flight/fight reports of these 2 aircraft in Real Life that took place at the same altitudes of on the deck or under 3k/4k to have a more correct comparison to RL......
hope this helps