Casual ain't dangerous. In fact, advanced isn't dangerous nor should you be afraid of either of them. The mods don't move RPs about without good reason. That someone who is not the GM thinks it doesn't "fit" in a certain section is not a good reason.

People do not always take part in just one RP. That they are online but not posting in one thread typically means they're doing something else, like reading or posting somewhere else. In advanced, posts can go from many in a single hour to one in a month without the RP dying. 

If it takes more than a week in a casual RP without any activity IC or OoC or on other channels without prior notice of why, then there might be cause for concern, but it doesn’t mean the RP must be dying.

The key difference between the sections is not merely post lengths. It is also the level of thought behind each post. Where a free post might just cover a minute or two IC (we're guessing a bit here, not playing in that section), an advanced RP post can frequently encompass several hours (or even more) of IC time.

Some advanced RPs actually spend more time planning things than they do posting. Its simply a different style.

If you want to feel more comfortable with writing more we would highly recommend simply reading an RP from one, or both, of the "higher" sections. That might also inspire you a little.