You know after getting lv10 of concentrate I’m actually decently suprised at how much better it is at lv10 vs lv5.
As you are all aware, concentrate has a limited amount of hits available even though the duration is quite long at 45 seconds.
One of the arguments is that you can only use concentrate until you use up the number of hits.
However, after I ranked up concentrate to lv10, the tooltip says 20 hits btw (not 19 as per ToSBase), I find that it is actually almost impossible to use up all 20 hits within 20 seconds (since you don’t have to wait until 45s to recast it, you can recast it after 20 seconds).
The only way I have managed to use up all 20 stacks of concentrate in 20 seconds is to keep using auto attacks against a dummy, and even then the downtime is only a few seconds. Because I mean, you can only get so many auto attacks out in 20 seconds, it’s not gonna be MUCH higher than 20.
Also, a little known fact is multi hits in a skill only uses up 1 stack of concentrate.
So therefore, concentrate is an always-on buff much like gungho, except without the defense penalty at lv10+, and it is higher damage.
(Still pitiful btw, since it won’t scale, but is VERY decent for low levels)

and get to next job and it is your ONLY attacking skill.