First thing that is very noticeable is the sanding marks going across the grain. The correct way to sand is with the grain, never across it. Also fine, medium, course grits mean nothing. You should go by the grit numbers. If the sandpaper you are buying doesn't have grit numbers don't buy it. Quality sandpaper is important, don't use the cheap junk.

Now to fix your door. This is how I would do it.

Strip off what is on there with a powerful stripper. Environmentally safe or no smell strippers don't work. Put it on, let it soak, remove with a flat sharp putty knife. Do it again, this time brush with the grain with a stiff synthetic brush. Wipe off with whatever solvent the stripper can recommends. Wipe down again with clean solvent.

Now for the sanding. Start with at least 120 grit, maybe even 100. For this step you can use your sander. Sand with the grain. Once the door is completely sanded with either 100 or 120. Vacuum it off and sand with 120 or 150, depending what you started with. Vacuum again. Finally finish up sanding with 150 or 180 (again depending on what the previous grit was) using a sanding block with a soft backing. I use a wood block with 1/4 felt glued to it. Don't move to the next step until all the sanding marks from the previous step are gone. (grit sequence is 100,120,150,180,220, and on and on.)

As you have found out, sanding is the most important step to achieving a quality finish. Short cutting it and using poor quality sandpaper won't get you there.

One more thing. Since you are using an ebony stain, you don't need to use wood conditioner.

Good Luck