They built 380 Hornets. 11 were rebuilt from F3 to FR4. A small but credible force.
They only built 37 Do 335's. Deliveries to combat units commenced in January 1945. When the United States Army overran the Oberpfaffenhofen factory in late April 1945, only 11 Do 335 A-1 single-seat fighter-bombers and two Do 335 A-12 trainers had been completed. These were production units that maybe got delivered and maybe not all. The rest were prototypes and test birds. There is a picture in Wiki showing the ramp at the Oberpfaffenhofen factory when it was taken with 9 Do 335's, only one of which looks like maybe it could be made to fly, though some pieces are missing. The rest are minus engines and major pieces of airframe, so at least these nine were never delivered, and the picture caption does not say if the nine were test birds or production units. That leaves 28 possible birds, with 11 production fighters built and 2 trainers. That's less even than the Ta 152's, of which never more than 25 of the 43 delivered were in service at any one time.
Performance-wise, the Do 335's speed was almost identical with the Hornet at 474 mph to the Hornet's 472 mph. But the speed of 474 mph was only with emergency boost for a few minutes and was 413 mph on what we would call military power. It supposedly had a 721 mile combat radius at half load. The Hornet had a 3,000 mile range which equates to a 1,500 mile radius with probably a 1,100 – 1,200 mile combat radius. Interestingly, the Hornets with 1,770 HP per side were the fastest variants at 472 mph. The NF21 with 2,030 HP per side was the slowest at 430 mph and the PR22 with 2,070 HP per side went 467 mph. Naturally, these Hornet speeds are at max boost, as with the Do 335, but it was faster at military power than the Do 335 by a margin.
If you dig around, you can find an initial climb rate for the Do 335 of 4,600 feet per minute, but they don't tell you at what weight that was recorded. The Hornet can be found to have a climb rate of 4,650 feet per minute with the same caveat. The people reporting these data obviously aren't thinking about analysis by someone at a later date.
Wing loading for the Do 335 at 25,800 pounds is 43.6 pound per square foot. At the empty weight of 16,975 pounds it was 28.7 pounds per square foot. Combat wing loading was in between the two. I'd estimate it was probably in the 38 – 40 pounds per square foot range typically.
Wing loading for the Hornet at 19,500 pounds was 54.1 pounds per square foot (NF). At the F1's normal weight of 16,100 pounds it was 44.6 pounds per square foot. At the empty weight of 12,502 pounds (F1) it was 34.6 pounds per square foot. The heavy Hornets were the night fighters with radar and antennas. I'd estimate the fighter variants at 38 – 40 pounds per square foot typically, without drop tanks (or after dropping them).
On paper they have close to the same speed, climb about the same and the Do 335 has a possibly lower wing loading, but maybe not by as much as it might seem at first. The Do 335 SHOULD be able to roll better, but I can't find any data to support the contention. I also cannot find any CL data at all for either aircraft.
The Hornet had four 20 mm cannons and the Do 335 had two 20's and one 30. Call the armament a wash.
But with something like 28 Do 335's perhaps flyable and something like 11 or less production units completed and maybe delivered, the Do 335 must be considered against 380 Hornets delivered. If the types had met, the Hornets would have overwhelmed the Do 335 if only by virtue of there being 10 times more available, all of which had longer range. Even if the Hornets couldn't catch the Do 335's, and it is probable they could after emergency boost was used up, they could certainly follow them (or it, if only one) until the Do 335 had to land or become a glider. I'd say advantage Hornet in the real world with the comparsion being essentially unkown in a one-on-one mixup.
Sorry, that was not a best twin dogifghter response, it was copmaring the Hornet with the Do 335 ... I didn't mean to wander, but noticed it after I posted and figured I'd just leave it in for postetrity.