"In standard dance, in order to make a large forward step, it seems necessary to slide a few inches on the heel of the forward foot while the leg is straight, before rolling down the whole foot. Is this correct?"
Generally this happens because you've put the foot out too far ahead of your body. We all went through a phase of doing that.
Hopefully as your skills and strength mature you will be able to project the body more into the steps. The leg will still swing a bit ahead of the body right as it's placed, but not so far, and in a way that it feels like the foot is landing in the "footprint" of the body - basically it will feel like the foot is "underneath" where your body's forward momentum would cause it to fall if the foot wasn't there to catch it. The result of this is that your weight will arrive in a way that sticks your foot to the floor rather than skates it on the back edge of your heel.
For now, spend some time just walking naturally in front the studio mirrors, not trying to dance. In fact, walk around a bit without even looking to get your action natural. Then start looking and notice how your heel lead develops only at the last instant of the leg swing. Dancing works the same way - it's just ultimately bigger because we move our body more. But as beginners, we get stuck trying to reach our feet into over-emphasized unnatural heel leads, and that's where the skating comes in.
Dance is ultimately about moving the body. The feet are just there to carry it.