Getting back the original.
.. ie. artillery pieces that have the barrel length of some 30-35 calibers. Granted, this is a bit longer barrel than on the pieces that can be called like that. like the Soviet ML20, or the British 25 pdr, but bear with me for the duration of this thread. Artillery 'niches' are of 88 mm, 105 mm, 127/128mm, 150mm, and 170mm, with MV of some 650-700 m/s maximum. Max elevation is still above 45 degrees.
The 'no free lunch' rule will be evident - for the same weight vs. the howitzers, shell weight is going to be lighter, but the range will be longer, and so will be the ability to hit the moving targets that come in close, talk to about 1000m. Lets stipulate that Heer has no problems in specifying the 88 gun-howitzer as the backbone of their artillery park instead of the 105 mm howitzer (this is the hardest part probably, since the 105m shell was at least 50% heavier, even if that howitzer was short - if not very short - ranged). Or, go with 105mm gun-how for the motorized or mechanized divisions, and 88mm for the non-motorized units?
The dedicated guns are still being made, like the AT guns, or the long-range guns. They look at piggy-backing on the KM and LW guns for the long-barreled pieces, in order to save time and coin.
Will the Heer artillery park will be better off, or worse off?
The Germans had decided to go with the 10.5mm Howitzer in the 1920s and/or early 30s. The US had decided the the same thing in the 1920s but the US didn't go into production until around 1940.
The Germans kept the 7.5cm for the infantry guns, the mountain guns and for the guns for the horse cavalry. There were 18 regiments of cavalry in the 1930s.
Due to chronic shortages 2nd line infantry units got left over 7.5cm guns from the end of of WW I or the 1920s. Also due to chronic shortages they Germans issued a fair amount of captured equipment, usually to 2nd, 3rd and 4th line units. The Germans did have some standards as to which units got which artillery pieces based on existing ammo supplies. If there was too little captured ammo they scraped the guns rather than even use them as fortification guns.
The Germans had done a study and found that a 10.5cm shell was over 6 times more effective than a 7.5cm shell, which sounds impressive. It is, but not quite by that much. Since the 7.5mm shells are lighter you can carry ( load the wagon) more. And the 7.5cm guns usually fire faster. This makes up for some of the difference. But fuses are expensive and so is the labor to make the smaller shells/casing. Cost is not directly proportional to the weight of the materials.
Artillery is rather manpower and transport intensive. A German four tube 10.5cm howitzer battery included 4 officers, 30 NCOs, 137 enlisted men, 153 horses and 16 towed wagons.
Many of the wagons were ammunition wagons and the battery could carry 336 rounds of ammo in their own transport. They also had a single If.5 machine gun cart.
I will note that the 336 rounds of ammo will only last a 4 tube battery 21 minutes firing at 4 rpm which is about 1/2 the max rate of fire.
The 8.8cm gun howitzer battery can carry more ammo and have more range.
Wither the 528 (?) lighter shells will have the same target effect is subject to question, and not all the shells are going to be HE. There are going to be some smoke fire missions and possible illumination missions.
Now the Germans, like a lot things, were rather late in getting into mass production and this thing.
didn't get into mass production until 1943 (1872 built) and in 1944 outstripped all the old 10.5cm howitzers ever built(7807 built in 1944).
The muzzle brake allowed for slightly better range but the converted AT gun carriage cut about 5 degrees off the elevation.
It was a bit lighter than the standard 10.5cm howitzer.
There is a lot that goes into artillery when you start figuring in manpower and cost of production and especially cost of ammo (and transport).
The 8.8 cm gun/howitzer idea may have number of things going for it.
I have doubts about going to the larger sizes, although a 12-12.8cm howitzer may have some appeal depending on desired transport. Going too far for range may just give a light shell 15cm howitzer as far as moving it goes.