anyways, is there anything else you would recommend.
even in database i see the comments are saved according to component (eg: com_sobi, com_gallery) and not category.
It does not matter. In SOBI2 each entry can belong to several categories, and if we know the ID of entry, we can get a list of categories to which it belongs. But just such behavior does not correspond to the JComments Latest module logic. This reason I say that solution is creating some new module.