The buildup on a direct injection engine is much larger, harder, and sticks to the valves with greater force than a port injection/ carburated engine. I have seen the buildup in the 7/16" range on a 1.25" valve. It either has to be cleaned manually, or with a some liquid introduced into the intake. The latter of the two being less effective, but obviously easier. Revving up the engine will either take small particles off or large iceberg chunks, that will not go through the valve, and may get stuck.
Then there's the added weight of that buildup on a valve, opening and closing 3000 times per minute, hopefully the spring is up to the task of pulling the valve back in place before the piston takes the same real estate.
As stated before in heavy buildup instances, manual scraping and vacuuming out is needed