You don't need to wait for LL to get to 5 stacks, once you hit it, if the totem is smart enough to keep attacking that target(pretty big if considering how stupid this stick is) your next LL should be hitting a 5 stack. The totem has a cast time under 2 seconds. So after that first LL hits, all the rest should have a full stack behind them.

The reason it is so little is simple:
Melee damage is affected by armor, glances, and hit. Unless you manage to hit cap for 24% melee hit, you will miss some. The armor makes that damage lower. Glances will lower damage as well.

Now look at all the other things on that list.
Lava Lash hits like a mack truck.
Lightning Bolt shows up a lot thanks to MW.
Windfury is showing up for more.
The normal flametongue is sort of an autoattack, but is not melee damage.
flameshock and earthshock are both just doing their thing.
Just keep going down that list....

The big issue is that if you look, how much of this is active damage vs passive.
Auto-attack, Windfury, flametongue, searing flames all of these require no more than 1 button push (searing flames is a bit more active, but is not even really 100% controllable)