Artillery are not all that great on offense, because they do not offer the hitting power and skew and flexibility of infantry and tank based forces.
For example, if you have 10 infantry 5 artillery, or 10 infantry 4 tanks, one has a punch of 25, the other a punch of 22.
However, once the FIRST force loses five infantry, it starts losing 2 punch with every casualty. The second force only loses 1 punch with every casualty until after ten infantry are lost.
Also, tanks are far more flexible, and can move faster.
I generally do not see more than about six or seven German artillery as useful, because I can’t keep enough infantry alive to keep that many artillery useful.
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Also, at some point, I am pumping out mostly tanks with Germany. Steady stream of inf/artillery do NOT offer flexibility, unless you have a load of transports, which I usually do NOT have with Germany. Tanks let me switch my attacks around, and ALSO let me reinforce the front line faster.