I would argue that you're looking at those "design notions" through your personal lens, based on your needs, and so you don't see the improvements. Others of us clearly see them, and have even already experienced them. The LE in my Haiku is at 1.4 amps and it heats up quite quickly, even through the less-than-optimal thermal path in that head. This larger Mahi head handles that heat much better, I can really tell the difference. Plus on top of that my candela increases 34%, which is probably a big deal to many who need that.
So while I agree with you that it doesn't replace the Haiku, I'd just argue it wasn't intended to. Its a different product, for different uses. Its not for everybody, but its definitely for some of us. I really like it.
Also pic, because its pretty too