Yes, because it's unbelievable to have 1/10 (11.000.000 vs 1.800.000 rays!) of the speed, just for a single shader.
I'm sorry, but right now, your nice script, it looks like unusable in real production (cause the slowdonw)
Maybe, it's an idea to make an external software and a bridge from this software to Max.
So, anyone can use your software to create a nice bitmap (Diffuse, S, B and Disp)
Well, I appreciate your honesty, but I disagree with your statement that Walls & Tiles is unusable in real productions. Hundreds of customers (I won't disclose the exact number) use it in real productions (mainly vray though) and create stunning renderings with it. In vray you´ll also notice a slowdown (I haven´t measured it though) and yet it´s very usable for many.
If you ever created a more complex shader with several nested maps, you will know that these shaders are slower to render in general. If you are used to only using simple bitmaps, of course it´s not slowing down the rendering as much, yet still considering a slowdown of 34% (referring your comparison of no bitmaps vs. loaded bitmaps).
I think you miss some benefits of Walls & Tiles if you suggest to use an external software to create the bitmaps and then use them inside of 3ds max: Walls & Tiles is made for flexibility. You wouldn´t have this flexibility, plus the possibility to save a lot of ram on high resolution textures, if you would use just a replacement of bitmaps with an external editor. Walls & Tiles is half-procedural (using bitmaps and random distribution), which means that it generates large scale textures on the fly while rendering, yet only using the RAM for the single loaded bitmaps. This is the real clue of the product and it wouldn´t be possible with the way you suggested.
Nevertheless, I understand your concern and I promise to think about this and look for optimization. No software is perfect, not even 3Ds Max as we all know ;)