Well, I spent a number of years writing drivers for PC systems. Some years the I/O chips were faster than CPU, and some years the CPU was faster than I/O chips. DMA was usually slower, just because release cycles for CPUs tended to be faster than release cycles for I/O controllers. Eventually, most driver writers decided that it was usually better to use CPU, even if the I/O controller was faster. That way, when the CPU got upgraded, you would automatically get a speed boost. While programming an I/O controller was both more arcane and more more likely to require a complete reimplementation in a couple of years (as well as customer complaints and market share losses.)

I'm not saying that things are the same today - but it kind of sounds to me like they are. Back in the days, people were always claiming that we should switch to the newest and fastest I/O controller since CPUs were more general purpose and would therefore always be slower. It just didn't work out that way in practice.