Actually they are crediting the aggressive killing of the snakeheads with keeping them in somewhat check. Despite this aggressive removal of the snakeheads they are still here and as previously stated, they are here to stay. They are not going anywhere but if left unchecked other species may. It's really that simple.
While zebra mussels have made the Great Lakes water clarity clearer they have "unleashed ecological havoc" and are "sucking the life out of Lake Michigan and lake huron" according to the experts. That doesn't sound like a plus to me.
If by sucking the life out of the lakes you mean contributing to a crash of alewife (invasive) which contributes to a crash of Pacific salmon and steelhead (introduced) I guess you have a point.
However none of those species are supposed to be there. In lake Huron, native species are doing better population wise than they were prior to the alewife crash (which was probably caused by zebra mussels). The great lakes are a great resource, and lots of fun but the trout and salmon fishery is artificial and dependant upon stocking.