the 'experts say its ok' because its proven to be best for the animal, not just because it gets the job done. cgd has everything they need to be as healthy as they can be. feeding live is fine, but as a treat more than a staple. muscles come from alot more than hunting food. give them enough to do in the tank and take them out let them run around theyll get plenty of stimulus. but it sounds like youre generalizing all/most reptiles in your reasoning. whats best for some does not make it best for all. look at something like the iguana. are you going to tell me they lack muscle and stimulus because they dont eat insects? or would you simply toss a dozen crickets in there to hold true to your beliefs? (I always intend to feed any reptile or amphibian insects, because animals need stimulus to be healthy, just as much as vitamins.). disregard any general knowledge you have for a moment, and learn about just the particular animal you are looking to get, theyre not all the same.
a dozen or so of my cresteds wont even touch live food, and theyre no less healthy than the ones that do.
i use substrate on everyone over 10 grams, usually eco earth or coco noir in the non planted tanks, and peat moss/soil in the planted tanks. if you plan to plant a tank you can always grow a ground cover to limit the risk of ingestion. i have grass in one of my tanks, theres plenty of other options, and they look nicer than just dirt.
the leaf bug thing is interesting. im curious to know if/what of those are safe