I still don't understand 'hard/soft' after reading this thread, anymore than I did before reading it.
As to yoshinkan, it is a PRECISE style of movement, and a pedagogical method. I wouldn't define it as hard. It does tend to stress the martial aspect, but then so do teachers like Chiba Sensei.
In terms of sweat, the Aikido Kenkyukai group trains harder than most I know (hours at a time, no talking, much suwari waza, lots of sweat), but I'd bet most 'knowledgable' people would describe their technique as 'soft' (right up until the time you hit the mat anyway).
I've heard styles described as
What exactly is this soft? what exactly is hard?