The new growth is not draining energy from your
plant. The growth hormones are concentrated in the
growing tips so that is where all the new growth is. Constant pinching will sometimes cause the growth hormones to move lower in the stem and cause new branches, but that is rare with an Arboricola.
To get new growth closer to the main stem, you have to cut the existing stems back to that main stem. In fact, that is what someone else did to get the side growth that is on yours.
Fungus gnats emerge from the gnat larvae that are in the top layer of the soil. The winged adults only live for about a week and then die on their own.
Remove and discard all loose suface soil from the
plant, getting right down to the top of the rootball. Also get rid of all the moss. Be sure to allow the top quarter of the rootball to dry in between waterings. Not only is that better for the
plant, but the larvae cannot survive long in dry soil. Adding a thin layer of sand on the surface of the rootball will also serve as a deterrent to the gnat larvae.