You've already basically got the idea of "genetically tractable": if we can readily modify an organism's genome using known techniques, then it's genetically tractable.
That's a moving target, of course, because the set of available techniques is constantly expanding, so this is more of a pragmatic definition than a taxonomic definition. It's a ...
If the query genome is unknown, a microarray cannot be made for a target species. Microarrays have DNA fragments of what you want to amplify on them. Those fragments must be known.
DNA microarrays are microscope slides that are printed with thousands
of tiny spots in defined positions, with each spot containing a known
DNA sequence or gene.
What it seems you're struggling with here is a lack of clear definitions.
Yes, the unity of core cellular mechanisms implies an unbroken line of descent back to the origins of life. But that does not in any way mean the cells are actually the same. I think that you would find it instructive to learn about the puzzle of the Ship of Theseus, which is the ...