Then this is not genuine bending anymore, then the avatar is simply using different bending arts in short sequence. Narutowise that would be the same as using an earth jutsu and then a fire jutsu to make some pseudo lava, not using the lava element. In reality it's something two different benders could accomplish, something that even has occurred a few times in the series. They once used a cloud camouflage with air- and waterbending.
Not to mention some of the things you said can be done by regular benders. In the old catacombs of Ba Sing Se the Dai Li was bending crystal. It's very well possible that regular earth benders can bend diamond, but the truth is what would be the point of that? They can only bend, not create, so they would have to be fighting in a diamond mine and you don't find those very frequently and even if that was the case, diamonds are really not big. So it's essentially useless.
There was also a swampbender who could bend vines, which is in fact plant bending. However that was only possible because of the large amount of water in the vines and the flexibility of the latter. He was bending the water, not the vines itself. Trees are much more resilient and have way less free water in them. It's the same principle as with metalbending which is based on bending the impurities in the metal. The more impurities, the easier it becomes to bend it, but the less quality the metal has. The higher the quality, the less easier it becomes to bend it due to the lack of impurities. It's the same with trees. Vines are still doable, but trees are far more difficult.
You're thinking way too much in Naruto terms about the concept of elements, while it's quite different for TLA.
Anyhow I've always expected for airbenders to be able to create near perfect vacuums. Some techs even started to approach like how Zaheer sucked the air out of people to choke them, but in the end it never really came to be.