"Got 'em on TCAS" isn't an acceptable response to ATC. "Traffic in sight" is acceptable, as is "negative contact." But not "Got 'em on TCAS." That doesn't mean a lot to a controller, nor can the controller be assured of what you've "got" on TCAS.
Can the controller "be assured of what you've got" when you report "traffic in sight"? Moreover, can the controller be assured that it will
stay in sight?