The life span of the Jumo engines was in 10 s of hours, due to lack of suitable heat resistant additives to the steel blades, limiting the use of many aircraft. fuel shortages also hindered their use.
Actually this is only true for the powerplants built in early 1944, when it was still largely in prototype stage. By late 1944 the Jumo004 had a lifespan of 50 hours, thanks to improvements (i.e. turbine baldes were now hollow and thus more heat resistant).
The many designs and high quality research of the Germans did not lead to any weapons usable in the war.
Don`t let yourself blinded by the popular and mythized "secret weapons".. there were many many "conventional" design aparts from them, which proved to be very useful on the field. New radar, passive homing devices, smart bombs
The german industry basically failed to introduce new designs in any quantiy.
How about Me410, Do217, Me262, He-177, Fw190? They were all new designs, and produced in rather large quantities. The "old" models were continously upgraded with new engines and weapons, so they too remained among the best.
The Ju87 and He111 designs, were at best obsolescent by the middle of the war and required replacement within the German air strategy. no new dive bomber was introduced.
A comparison of allied medium bombers shows the German designs falling behind in terms of speed range and bomb load.
Hun? It was actually quite the other way round. While the Germans were behind the Allies in standardizing a 4-engien bomber in numbers, their medium bombers were simple the best the world known at that time. The He-111 had a bombload of 2500kg, later ones went up to 3250kg, the Ju-88 or 188 could carry 3000kg of bombs, to a comparable range as Allied mediums. But those carried only about 2/3 of that bombload, the B-25, B-26, Wellingtoncould carry no more than about 1800kg during their carreer.
Speed goes similiar. The He-111 was comparable to Allied medium bomber designs with it`s speed of 430 to 480 km/h, depending on model. The JU-88 was faster at 470 to 500km/h speed, and the Ju-188 was really impressive with 545 km/h.
And if we compare allied mediums to the largest german 2-engiend medium bobmer the Germans had, the Do217, it`s very unfavourable to the former ones. The Do217 could carry 4000kg of bombload, at 515 km/h max speed, and plenty of defensive guns for it to a respectable range. It`s a less known aircraft though.
The dedicated ground attack aircraft requirement produced the Hs 129 built in small numbers and suffering from problems of unreliable and easily damaged engines and some vision problems. The Fw 190 was successfully adapted to the ground attack (fighter bomber) role.
You could safely add the later Ju-87s as well, as those were more like dedicated ground attack aircraft than dive bobmers, as shown by the fact that they no longer had dive breakes, forward firing cannon armament was introduced, cluster bombs, strafing gondolas were carried, and the whole plane, engine and crew positions were heavily armored.
The germans did not produce an effective and common answer to the high flying speedy Mosquitos
First this ain`t true, as they had produced the Heinkel 219 Uhu high-speed nightfighter for that purpose in some numbers. But the Mosquitoes were never as much of a threat that would justify the full scale production of such a specialized plane. Fact is, the Mosquito was a useful light bomber for ground attack and anti-shipping, but as "strategic" bomber, it was merely a propaganda weapon of little actual value, thrown in to the bombing campaign in numbers after the RAF-BC had to realize that it could not keep up the bomber offensive due to heavy losses in early 1944.
The transport units still depended on the JU 52/3m at the end of the war despite its problems with difficulties in loadig it and its low performance compared with later US transport aircraft.
Ju-52 obsolate? No. It remeined the most dependalbe transport of the LW, in fact some Ju-52s still fly in Switzerland in commercial role. I don`t think it would have a low performance compared to any other transport of it`s time.
As for transports you shouldn`t forget the huge Me321 and 323 Giant transports, they were the the equivalents of the USAAF`s Hercules transports at that time. They could carry loads far in acces of any other transport of their time.
The British continued developing the pre war Spitfire throughout the war.
Other "shitty " aircraft as ChristopherPerrien put it were successfuly replaced and in quantity. Does not this show the British aero industry in a much better light than the German.?
Overall the Germans had good pre war designs and many quality designs and much high quality research at the end of the war. However it did not for the most part replace older obsolescent designs during the war in any great numbers.