I will say this about your edge appearing to have uneven thickness from one side versus the other. Two things may contribute to that. The easy one, or at least the one you should be hoping for, is that you're not holding the knife at the same angle when you're grinding it on the left side versus the right. The Work Sharp belt sharpener isn't foolproof, and I haven't found the guides on mine to be very good. It still takes a decent bit of technique to get a consistent edge out of it, and even then it's highly dependent on the bevel on your knife.

So option 2 is that the grind on your knife isn't true. Not the edge, which is easy to deal with, but the actual taper from where it's flat to where the cutting edge starts. That's not uncommon on cheap knives, and it'll exacerbate problem #1, above, if you can't compensate for it. It's hard to eyeball but you can suss it out with a digital caliper or a micrometer and a straight edge, if you're careful. If that's the case, it'll never be right. You can make the apex of the edge true to the centerline of the blade, and with a decent guided sharpening jig you probably will. But it'll always visibly look like it has more meat on one side than the other, because it does.

If I were you, I would reserve the belt sharpener for edge angle reprofiling or heavy duty un-fucking of a blade that's got major nicks or chips in it. I have one, and I haven't found it to be a good general purpose sharpening solution. I much prefer my Work Sharp guided bench stone or, ideally, my Spyderco Sharpmaker for actual decently precise sharpening of any of my knives that I give a fuck about. The belt sharpener will leave a major burr on your edge, and it'll always tend to leave the same burr on the same side because as you have correctly observed the abrasive passes over the edge in one direction on one side and the opposite direction on the other, and it isn't a tool very well suited to knocking that burr off. You always wind up having to finish it with a regular stone if you want to wind up with a decent finished job, and it always takes more work on one side than the other.

And this is coming from a bird who uses a fucking Harbor Freight belt sander to grind swords and bush choppers, machetes, axes, and mower blades. Such things have their place in the world, but fine cutlery usually isn't it. When belt sharpening, you always want to have the abrasive moving from the edge back towards the spine, which when you're freehanding on a belt sander you can do easily by just flipping the blade over. Not so on the Work Sharp.