but larger and smaller dogs being able to reproduce together does not support the evolution theory.
Sure it does. It's evidence that all dogs share a common ancestor. And it certainly disproves your "two kinds of dogs" theory, at least if interfertility is your basis for "kinds", as you seem to suggest.
Besides, the larger and smaller animals still need "help" with their breeding. You can't expect me to believe that, thousands of years ago, a st. bernard ancestor and a terrier ancestor made the first 'batch' of a modern species of dog on their own.
I'm not sure why you state this. It's more accurate to say that both the St. Bernard and the terrier share as an ancestor one domestic "breed" of dog, whose more distant ancestor was also the ancestor of modern wolves, coyotes, and foxes. Given the power that selective breeding has on influencing morphology, I don't find it unreasonable to assume that a "medium"-size, wolflike dog couldn't have given rise to both large and small dogs which we see today.
Also, 'kind' is defined as whether or not they can reproduce. if they can bring forth offspring on their own, without any 'help' then they are the same kind of animal.
Ok, this is a crucial distinction - can reproduce, or do reproduce? For instance, tigers and lions do not, as a general rule, mate with each other in the wild, because due to behavioral and chemical differences they just don't recognize each other as mates. But if forced to mate, they do produce viable offspring.
The point is that reproductive isolation happens for a number of reasons beyond geographical separation and genetic incompatability. Sometimes isolation is as simple as behavioral differences that cause the organisms to not recognize potential mates. Or coleration differences with the same effect. Or even pheremone differences. Sometimes it's structural isolation - the first organism's Tab A won't fit into a potential mate's Slot B.
If you're going to draw the "kinds" line at genetic interfertility, then you admit there's still some 80,000,000 "kinds" or so. (This has a reprcussion to Ark arguments, but since you haven't raised that argument, we won't go there.) And you have to be aware that we've observed populations of species diverge to the point where they were totally, genetically incompatible with a species that they used to be interfertile with. By your definition, new "kinds" are appearing all over the place. This would appear to contradict your "original, created kinds" argument.