1st: it's not because the plane is a little bigger that the airframe is less capable of withstanding high G's. The Stuka is bigger than a 109, but more or less the same size (and lighter) as a P47, for instance. It depends on the purpose of the plane, and it's sturdiness, the way it was built.
This is truth to some degree.
However the smaller the plane the easier is to make it sustain higher G loads (once again, light aerobatic planes can sustain the highest G loads). Once the aircrafts get larger and heavier they need heavier airframe to make them capable of sustaining higher G loads. This strengthening adds weight by itself, and starts a vicious circle of weight increase.
During the war there only two medium bombers capable of diving more than 60 degrees. These were Ju-88 and Tu-2, two absolutely remarcable planes (Ju-88 could dive up to 70 degrees). These bombers had a very strong airframe. For the rest of the medium bombers flock, it was considered unfeasible to strengthen them to withstand the G loads of such dives.
From heavy bombers only He-177 was capable of 40 degrees dive.
In conclusion the heavier the plane is the tougher it is to make it withstand G loads.
Warlordimi wrote:2nd: It was when you said "not obsolete". For me, the Stuka WAS obsolete because it was underpowered, outgunned, even when the war broke out. And it went even worse as war passed. I don't think you could consider it as "not obsolete" because the germans just never found anything to replace it. Like other planes in their purpose(Ju88, Ju52...).
When you say "Stuka WAS obsolete because it was underpowered, outgunned, even when the war broke out" you make it sound like Stuka pilots did sorties to chase Spitfires. Stuka was a bomber not a fighter. What is underpowered for a fighter it is not for a bomber. Il-2, Ju-87, Hs-129 had the same powerloading, this was the standard for attack planes. D-5 wasn't outgunned compared with other attack planes, 2x20mm was good enough, earlier versions were not attack planes, but dedicated dive bombers, there was no need for larger caliber guns. The fast firing twin MG-81 mount was quite discouraging for fighters.
Ju-88 was a new plane, still in development during BoB. It became one of the most prolific and successful ww2 planes. What do you mean they did not have anything to replace it? Why did they have to replace it?
Ju-52 was a very good transport plane, with excellent field performance. It was as good as DC-3, I see no need to replace it.
In general Luftwaffe's planes were among the best in their class, if not the best, for the duration of the war. The only Luftwaffe plane I would call obsolete is He-111, but after BoB it was used almost exclusively on Eastern Front, where it met little fighter opposition. Its reliability kept in service almost to the end, though mostly as transports in the final months.