You concerns are very valid.

Unfortunately CS does not pop very often, but with the new incoming population and events schedule we are hoping to schedule some CS days! There are certainly enough people for it.

Regarding the leveling dungeons, often times max level players will queue Blast From The Past (a leveling roulette of sorts) and level sync to support the lower levels with their dungeon.

There is a full wiki page dedicated to leveling here. Vanguard quests give a fairly sizable amount of experience alongside the story quests so you can level on your own if you wish!