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All other modern pieces had very low production number the most produced is the GebH40 with 420 pieces, yes i know this was a mountain howitzer but there is no reason (price excluding) that would not have been a good piece of field artillery (is the howitzer with the longest range in the list).
and all are in low band as weight (i'm no a expert but is possible that a 1.4 ton horse towed howitzer is more easy to put out to mud that a 2 ton horse towed howitzer)
taking out the parts i've agree with you (the most)
i just want add that 2 122mm round weight more of 2 105mm round but also are more powerfull, and generally a 122 weapon fire slower that a 105 weapon, so do not need the same number of rounds for the same work.
the threat was on pieces not on the armies