I've always been a bit perplexed about some of the choices the "luftwaffe" made (109 over he-100 for example)
I guess this has already been discussed elsewhere in this boards. But the main reason was that Germany couldn't build both the 109 and the He100. And stopping the 109 production run was out of the question.
The Bf109 won the official RLM competition for the single-engined fighter for the luftwaffe in 1936. Discussions about wether the He112 was or not better still run up to this day but I think the RLM chose the right model between the two. The Heinkel was much expensive to build both in economic and manwork hours and by the time the competition was held, it was so full of problems it simply couldn't compete with the bf109 in equal terms.
Later the 112 proved to be a potentially capable fighter, but the 109 had already won the competition.
The Heinkel 100 was a private venture by Heinkel, who was dissapointed and annoyed his He112 had lost the RLM competition. The plane itself was brilliant for it's time and the performances on paper look great. However, for the time the He100D was flown (the previous prototypes weren't adaptable for combat usage) the 109 series were already being built, and factory lines were devoted to it. Changing the factory toolings from the 109 series to the He100s was out of the question, as the Bf109s were being already built in too low numbers (even by September 1939 there were too few Emils in service, that quite a good deal of Doras were still in front line Geschwaders...) there was no chance the production had to be stopped to bring yet another completely new model into service.
One has to understand the point of view by then. The 109 was seen (Righly so) as an excellent fighter on it's own. Sure, the He100 had better performance (on paper) but that extra performance won't justify stopping the whole production run, retooling the factories and lose several months worth of fighter production. Seen on perspective the RLM did the right thing, IMHO, turning the Heinkel down.
There was no question at all of having both models in service. Logistics would've been much more complicated that way (having two models of a plane to do the same role is an unneeded complication). And besides, there never was enough DB601 engine production for both the Bf110 and Bf109 series, only to have yet another fighter using the same engine.
All in all this is the same story as with the Fw falke. The plane was simply brilliant and much better (again, on paper) than the Bf110s then entering service in the Luftwaffe. But the Bf110 was already in service and in mass production. And was good enough not to warrant yet another model to cover exactly the same role, and the 110s were also being turned out in too low numbers to allow for a complete stop of the production run, time and resources for retooling, and then putting the new model on the line.
as well as any true evolution in airframe design from 1938-42. Basically after the 190 everything is in "vapor lock" till its to late. From what i've read I always conclude that the decisions are being made "above" the luftwaffe.
There were quite a deal of projects, humble. They simply delivered nothing, or even worse, delivered nightmares.
The Heinkel177 is one of those examples, a plane designed to be a fast and excellent heavy bomber that turned out to be a flying gas can. The Me210 comes also to mind; the plane designed to take the Bf110's spot wasn't even safe to fly until late 1942 (by then it was quite a nice machine, but with a year and a half delay. The 210 number was so associated with disaster that the definitive model entering service with the LW was called Me410, even while the 210 gave sterling service with the hungarian air force).
The Me209 and Me309 projects also are there. The RLM was actively looking for a fighter to replace the 109 in the JagdGeschwaders. It turned out to be that the 109 had almost the same performance as the prototipes of both "replacements", so none of both entered production and the 109 soldiered on until the end of the war.
The whole "Bomber B" projects were a massive waste of an immense ammount of resources, times, and money, involving no less than four of the major plane builders within germany, that came to nothing because the intended powerplant those bombers should've used from 1942 wasn't still reliable by 1944. And so the bombers which were to replace the Heinkel 111 or the Ju-88 never existed, and the german bomber units, exception made of those equipped with the very good Do217, had to make do with the He111 and the Ju88 variants up till the end of the war.
There were many other instances like these, of course, but I'll stop here.
It's not there were no projects or no intentions to develop a "second generation" of planes since 1941, Humble. Those projects existed even before the war started. They simply came to nothing because so many reasons they are hard to list; but sharing one common denominator: industrial efficience under the Nazis was down to stupid levels.