When looking at this animation various things occurred to me.
Your animation has much more power now, but the character lacks in life, it looks stiff. That is because he doesn't use his whole body to move the "heavy" hammer. I tried an edit to increase his body movement to put more life into the animation (I used your old animation as a guide).
I think the animation looks more lively now, but the main problem is still there: The hammer doesn't look heavy! It reminds me of the
"fake-hammer" in One Piece. It's weight looks like 5t
but it's 2kg in real. The animation (body movement) itself is not the problem, just the hammer doesn't fit. To be honest, it looks more like he's playing golf.
But HOW do you make it looks heavy? Gravity! Look at your animation, but played backward (I had to delete the motion blur. Otherwise it wouldn't work).
Now you have a heavy hammer. And surprise, the timing is still the same! What do we learn here? Use the gravity to increase the power of the "slam" (and don't work against it like you do in your animation now). Just ask your own experience. Did you ever chopped wood? How did you do that? Use your axe, extend yourself, hold it as high as possible to put as much
potential energy as possible and with one blow you release all energy to chop the wood.
Use your experience and natural feel to put more life into your animation and make it believable. You went a long way but you can go even further. Be persistent!