I would agree that working digitally makes certain things more efficient, but I wouldn't equate efficiency with being "easy" in the sense that it takes little to no skill to get a good result.
I really don't buy this idea that doing things with efficient tools makes you lazy. It's difficult and inefficient to paint an oil painting with a live squirrel. It takes much more planning and finesse to use a squirrel than a brush, and you can only get a few strokes down with each squirrel before they bite your hand and run away. Does someone painting with said squirrel have no choice but to plan more beforehand? I suppose so. Are you therefore lazy to use a brush instead of a squirrel, just because it's more convenient and fairly efficient at certain tasks? Of course not. You use the most efficient, reliable tool you're comfortable with using.
It is true that lazy people do lazy things in a lazy way, but they also have lazy looking results. The most efficient tool in the world isn't going to let a bad artist produce a good painting from scratch. I can buy the best hammer in the world but I don't think anyone would want to live in any house I've built with it.
Nothing stops you from planning if you want to plan other than a lack of discipline. You still need to do some kind of planning if you don't want whatever you're making to suck. How else are you going to get a good composition? Plenty of people doing digitial painting will do numerous sketches and thumbnails beforehand. Likewise, as long as you don't care about the result, nothing is stopping you from going into an oil painting randomly, building it up until the paint is an inch thick.
You can scrape of the paint or push it around. I hit undo at most once or twice an hour, and by default only the last 20 strokes are saved. Most of the time if I want to fix something I'll just paint over it.
- Multiple versions
You want to test out an idea you're not sure will work, so you paint a thumbnail or make some sketches. Only difference in photoshop is sometimes you test things out directly over your painting.
Eh, if you're painting on glass or something.
- No knowledge of perspective needed - just bring up your perspective grid!
Won't do you much good unless you already understand perspective. In the real world people sometimes will use a projector or a grid printed on an transparent sheet of plastic, espeically for things like murals. What do you suppose people do for things that don't line up to the grid?
- Color mixing, color picker
Yeah you can rely solely on the eyedropper tool in Photoshop if you don't care about the final result. If you mean picking colors from the color selector (directly grabbing a specific hue or saturation) then I suppose the real-world equivalent would be buying specific pigments (eg. burnt umber) instead of mixing everything yourself from primary colors.
- No knowledge of anatomy required - just paint on top of your poser or daz model or photo ref without redrawing it!
Poser models look terrible, and a paintover by anyone who doesn't actually understand anatomy will look terrible as well. Also, what kind of satisfaction would a painter get from tracing over a photo unless they're just trying to impress the 12-year-olds on deviantart? In the real world, this can be done with projectors or transparent sheets of plastic, or via "camera obscura".