Every tool has it's purpose, and it's limitations. I carry one of these little guys:

in my truck for an emergency shovel (and have one in the wife's car). But in the winter, I also add a full sized snow shovel.

Around my place I have a few inches of topsoil over an incredibly nasty white clay (red river gumbo). A small shovel like that, or the trencher would do nothing. In fact, a long handled shovel does next to nothing.

If I need to dig a hole, I need to use one of these to start, and then scoop it out:


or, if I need a post hole, I have to use an auger. When I had the hole dug for my pond, the operator had to keep switching buckets. a small one with teeth to break up the clay, and then a big smooth one for scooping

That said, that little shovel has dug more than a few latrine holes with minimal effort while out camping, along with fire pits. I wouldn't want to pack a full sized shovel on a 10 day canoe trip, both for size/weight, and necessity, but that little one makes a few key jobs worth its weight.