I had never used one before, or any type of 'heavy equipment', but I was able to dig a 6' x 6' x 5' hole to bury a cow in the pasture where it succumbed. It took me close to an hour because of the 12" bucket, but I never thought it felt under powered.
A few months back during a dry spell, my clay subsoil about a foot below the surface got so hard I could NOT dig it. I could scrape it and leave teeth marks, but I could NOT get into the ground to get a bucket full. I could point teeth teeth down and raise the tractor, so it wasn't a lack of hydraulics. I was only trying to dig a bucket width trench though. Maybe if I had gone wider and tried a different angle, I could have made better progress.