Congratulations! I'm pretty confident you're the very first person to fully complete the game on hardmode. It's a huge achievement, especially considering how dark it is without a torch. Definitely a good idea to switch over to standard mode for now, since most of the upcoming updates will be focused there first.
And yep, the depth of the sand and sticky mud layers is intentional. They were even shallower in earlier versions (sand was 30, mud was 20), but I extended them a bit while still keeping them shorter than the other zones. The idea was to make those layers feel more like early-game obstacles, since they're light on resources and movement through them eats up more energy (horizontally). They're not really meant for farming, just a little terrain challenge on the way down.