Your problem really isn't stiffness. I mean yeah, stiffness isn't really considered a good thing, but I see outstanding replay makers who are really stiff.
Your replay making problem is that you're not getting your hits in a sequence or aiming for them correctly. You're just flailing around, hitting him wherever you can. Focus more on how quick you want the replay to be, where you want to hit him, and how to get the second most important thing about a replay...
Boomhits. PM if you want to know exactly what a boomhit is, but every good replay includes a boomhit of some sort.
Also know that good replays don't really matter on how many DM's are in it. It matters how you sequence every move together. Every boomhit, every decap, every twist, every turn, and so on and so forth.
Examples will be provided if asked. Good luck.