The copying process was quite a barrier to using compute (general purpose GPU) to augment CPU processing and you had to ensure that the work farmed to the GPU was worth the cost of the to/from costs. Game consoles of late have generally had unified memory (UMA) and it's quite a nice advantage because moving data is a significant bottleneck.

Using Intel's integrated video as a way to assess the benefits of unified memory is off target. Intel had a multitude of design goals for their integrated GPU and UMA was only one aspect so it's not so easy to single that out for any shortcomings that you seem to be alluding to.