I've been using OneCNC for several years now. I think they call it "OneCNC" because the developer liked an all-in-one solution himself. Imagine that, a developer who actually uses his own program to go out and play with his DMG
Of course, the Cadcam has to be capable of doing what you want for an integrated solution to be adequate. And to be clear, there are some free-form surfaces that I would have difficulty designing with OneCNC, but for the real world stuff I deal with, OneCNC has the tools I need for 3 and 4 axis work.
Using one system of course, could (should) make one very proficient at using all the software functions of that system to the max. After a while, you become so intimately acquainted with all the tricks and quirks that you can use it as easily as you use all ten of your fingers to type with
So IMO, simplification is better, so long as it works for you. Understanding what you are doing may in fact, allow simplification to work, rather than relying on a large assortment of gui icons to solve your problems by means of someone else's magic.
With the current state of OneCNC XR3, one could conceivably take any family of parts, create one program group, then import a brand new part (2d wireframe or 3d model or a patchwork of surfaces,solids and geometry) and update the existing processes to use the new model or geometry. You cannot beat that for convenience.
First you get good, then you get fast. Then grouchiness sets in.
(Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)