Well I don't know how you would classify "formally training" in hard style, but my instructor was a RKC master instructor. He taught "hard style" and did only a little comparing with fluid or "soft" style.
In my training, everything in your body contracted at the top of the rep. We did a drill called "tough love" where your partner punched or kicked you at the top of the rep. The blows could be in the quads, butt, gut, ribs or wherever. The point was to make every rep a full body contraction.
Fluid style, like in GS, is all about efficiency. You can't do full body contractions with 72# snatches for ten minutes. You have to get into a rhythm and a groove to make it work.
Someone explained it to me saying; "hard style is like running a 400 or 800 meter race, while fluid (soft) is like running the mile or the 5k. It all hurts, it just hurts a little different."
Did this help at all???