I want to second the thought that the tube doesn't look very roughed up. Further, the scratches on the tube seem to be mostly/only radial. When you rough up the tube, you want to use something like 180 grit sandpaper, and really get it moving around. You want scratches kind of every which way, so that you support grabbing power in all directions. When I am scratcing up my tubes, I not only twist the tube, but also move it around laterally as well, and try to make as many motions at once as I can. The end result is that the tube looks as much white as brass, due to the way it scatters light. Your glue should bond better that way.
As for acrylic. I don't know that there has really been any particular study on this, but my own anecdotal evidence, which now spans some years, tells me that acrylic paint DOES weaken the bond. I think that should go without saying, really... Its a layer of its own, that is not a glue, that separates the thing being bonded from the thing its being bonded to (tube to blank).
What I have started to do, is to tint or otherwise pigment my epoxy itself. You can actually use a small amount of acrylic for this, or there are other options. You don't want too much pigment in the epoxy itself, and you don't generally need a lot anyway...enough to make it mostly opaque though.
This provides the coloring to hide the brass color of the tube, but ensures that you have bonding agent fully in there between the tube and the blank to make sure the two are in fact actually bonded to each other.