I'm wondering if a slicing knife really does a better job than a chef's knife?
It does a better job of doing the things it does better, but it's not as good at doing those things it's not as good as doing.
What is it you want it to do?
If it's one or the other, if used skillfully, in most hands, a chef's is a better choice as an all around knife. However, a slicer is better for portioning, trimming and carving.
And whether it would be worth the extra cost and storage space.
If you're worried about "storage space" for a slicer, you have other pressing issues.
If you want one, it's worth the price and a slot in the block. I consider mine to be among my important and frequently used knives -- but that's me.
BDL