Concentrate lv 7 won’t make much difference from concentration lv 0. Concentration needs to be either maxed or left lvl 0. And even when maxed, Concentration works better for DEX builds than STR builds.
No. Cyclone doesn’t scale bad. It gives you 7% skill factor per skill point which makes people think it scales badly. But in reality, it still hits 27 times and has 2 overheats. Cyclone is by far the best AoE dps skill doppels have. The difference between lvl 3 and lvl 15 is a difference of around 55% more overall damage.
In fact, the reasoning of cyclone scaling badly is so flawed that if you calculate the proportional factor you get per skill point spent in Cyclone, you will end up having nearly the same prop. factor for spending points into Zornhau.
I can’t really notice an attack speed change and I’m honestly not sure if it works or not. Even if it does work, you shouldn’t bother too much with that since most of your skills don’t depend on attack speed (except Double Slash).