I have had similar issues. I love the clean top cut of a downcut on plywood. (I also have less clamping issues as it doesn’t “lift” the work piece as it cuts.)
But I wanted to get rid of the underside fuzzies as well.
I got a 1/4 compression bit, also known as a up / down bit, which is supposed to address this. The bottom is a upcut, the top is a downcut with it “compressing” in the middle.
I have not really had a chance to try it out fully, but it seems to work as intended. The trick, I think, is you have to make the initial cut depth be deeper than the “down” part of the bit? Which, if memory serves is a little over 1/4 inch. Before I upgraded my X axis I would be hesitant to have that deep of a cut (I think I am doing 8mm?) But with my upgraded gantry it can handle it.
The problem I ran into is I use VCarve Pro and you set the MAX depth of cut for a bit, but there is no minimum. So it happened to be breaking up the carve into layers less than the 1/4" minimum. I have now figured out how to set the layer depths manual but have not tried it out with the proper settings yet.
But even with the wrong settings it worked pretty good. I was cutting some plastic deck composite. The first layer was too shallow so it cut like a standard up cut bit, with the normal strands left behind on the top. Then on subsequent passes as the down cut portion passed over the strands it cut them away. So I wound up having a relatively smooth cut on both sides.
There were still a little bit of strands on the bottom edge but significantly less than I had with the downcut bit.
I am not 100% sold on it yet, but it is definitely worth playing around with.