I agree that Design thinking is inherently Holistic. But that said there is a lot of Design thinking that fails to be holistic, and that is why there is a lot of bad design. If Design thinking is inherently holistic, then bad design must be a perversion of Design thinking in some way. And that is where we come to various forms of reductionist thinking in design activities that disregard the whole being designed for some local factors like economy of scale considerations.
Design thinking projects a vison of the whole as to be realized artifact. But if we do not balance the wholes and parts in that vision, or we allow some characteristics to be given undue preponderance in the design process, then we get the distortions we see in designs of everyday artifacts that we live with every day. And this lack of design integration and the lack of expressive pattern languages has a profound deleterious effect on our lifeworld.