Frankly, complexity and piss poor design, crap just barely good enough to get by is all that is seen when we look at living things. The human is a great example, overly complex. poorly designed, sloppy build, light of no QC or error correction built into the critter.
Well, very inelegant designs by the standards set for intelligent designers with a particular set of limitations and a particular set of freedoms.
In the case of the intelligent designs we have limitations of cost and we have the freedom to start with a clean sheet of paper when we think that is a good idea.
In the design of a car we are not allowed to build millions of unique examples, sell them to drivers and see how well or badly they work. We have very severe cost constraints (not to mention legal ones).
In the case of the biological "designs" we have an unlimited "budget" we can make an enormous number of "mistakes". For example, it seems that more than half of ALL humans are mistakes and don't make it through the early stages of gestation. This is only a minor problem for biological "designs".
However, biological "designs" do NOT get to start with a clean sheet of paper. Nor can they "know" (in the sense of think through) what will work and will not so they are constrained to making small changes in something that is "known" to work. If an intelligent designer was so constrained s/he would be forced to produce some very messy intermediate designs even if s/he did know where they wanted to get to. Each new "design" must work and have a high degree of compatibility with the previous one.
These freedoms and constraints produce, again, EXACTLY the kind of designs we see in both human designed objects and in living things.
The designs are NOT so much crap as representative of what can be done within the constraints.
Human designs are less flexible than biological ones and do NOT offer the very large range of diversity we see in living things that are "ready" for a change in environment.