Centrosomes are only mysterious to someone who is looking for a reason to claim Intelligent Design. And of course as you point out the notion that the centrosomes are inherited independently of DNA is nonsense. That is like saying the egg itself is independent of DNA. It isn't. DNA determined its structure, including the centrosomes and all of the other organelles.
But I'm being told by some here, that everything outside the DNA that is needed is also specified by the DNA. It's confusing.
Well it is only confusing if you are refusing to accept that development is controlled by DNA. The only reason to take such a stance is not understanding the mechanism. But lack of understanding is not a basis for denial of the truth of the matter. There are lots of things I don't understand, for example how come all of the oak trees in a particular location "know" to produce lots and lots of acorns the same year and thus insure that the squirrels will only be able to eat so many and there will be plenty left over for making more oak trees. But that doesn't mean that synchronized mast production isn't under the control of DNA - obviously it is, as all oak trees are closely related in terms of DNA. However DNA is never the whole story. Genes are turned on and off by environmental cues, whether one is talking about trees producing mast or the location and age of a cell in a developing embryo determining whether it will develop into neural tissue or muscle tissue.
Here's something that I've wanted to know because it's related. Where exactly is the "3D geometry data" that defines for example, the shape of your skull, located? If cells need to differentiate themselves into structures like that, where is that specified? Sounds like membrane patterns and microtubule arrays according to Wells. But if those only come about under DNA control, then it's back to the DNA. But DNA doesn't hold "shape data" does it?
What makes you think that DNA doesn't hold "shape data"? My head looks like my Dad's head - except where it doesn't. Then it looks like my Mom's head. So I have my Dad's forehead, my Mom's jaw and my nose is somewhere in between. I can see the same thing in my daughters. Oldest daughter has my forehead and also over sized head - too bad for her, youngest daughter has my wife's forehead and normal sized head. Obviously DNA does control "shape data". Wells is full of crap.
Note - Just because we cannot necessarily identify WHICH gene or genes control head shape doesn't mean they aren't there. We see the results. Why should shape be any less likely to be under gene control than any other characteristic? Distinct lack of logic here.
Using the assumption that what Wells is saying is correct (and maybe it's not)
Isn't that what the argument is about? You really have to do better than that if you want to compete in an argument where sound logic is a requirement. See logical fallacy known as "Begging the Question".