Ok, thanks all (including Dev - I appreciate an "official" response) for the historically informations but I was thinking at this problem from a gameplay point-of-view, a german point-of-view to be more specific.
First, let's talk about mortar. Mortar is good on small maps, but this is the biggest RO2 map (for now at least) and here mortar is pretty useless. Just once I was able to win on this map thank to mortar - and that time was something very special.
Now let's talk arty. Arty on this map is good, very good if you know when to use it.
4 minutes cooldown for russians and 10 minutes cooldown for axis means that russians can use 4 artys in a game - standard round time of 20 minutes (theoretically 5 but you can't use arty instantly after the round begins, you have to go the radio etc ...) and axis can use it just 2 times. 2 times and 7 objectives to defend. This is very difficult, it shouldn't be like that. Russians already have the advantages of reinforcements, the obvious advantage of the spawns and now this ... I'm not saying germans should have the same arty times as russians but a tuning is needed. I think 6 minutes would be decent, germans could use 3 artys and 6 minutes is a normal time to wait - that 10 minutes almost makes you forget about having arty.