This is not a study.
Eh, unless I'm reading a different forum than you, he did summarise the argument. And summarise it over and over and over again. If you're too lazy to go further and read his sources, don't blame it on him.
Also, stop playing the professor. Big hint: it doesn't make you look good.
Because science is all about "proving" things?
Look, take these studies as data points on a huge plot. Yes, these may be just a few genes in a few organisms, but the more such comparisons are made, the more they illuminate about the relationships of the groups of organisms we are sampling.
We have a hypothesis about the family tree of these animals, which gives us predictions about the relative degree of similarity we should find between their genes, and people go out and test it. And test it some more. And then some more.
What exactly is backwards about doing that?
What are you asking here?
Do you mean what percentage of our genes has an orthologue in sponges and vice versa?
Or how much sequence similarity there is between us and sponges?
(Or something else?)
(
BTW, neither of these questions is trivial to answer, even with good quality complete genome sequences. Which we don't have for sponges as far as I can tell from a quick search in the NCBI genome database [the link leads to the list of sponge genome sequences in the database. All of them are mitochondrial genomes.])