It is the source of lag during the battles. It is not needed to see who is doing how much damage, just look at the HP of the base.

He's on about Level 3 bases where you still have damage caps etc maybe have the show top damager icon for level 5 upwards?

The amount or level changes nothing in terms of how much is going on. it's the simple fact that the page has to request extra SQL queries from the database that causes lag. That's why the button was added. With the button there's less update requests every second during base battles and it allows for less clogging clunk on the server so that people can actually continue to mass-hit the bases.
I too, hate the button, but it's needed with the game's mechanics to keep it lightweight on the requests.

might be a good idea to display a copy of the dmg list but simply not update it unless a update button is hit
and then use a seperate thing to keep track of amount of damage you are currently doing yourself(possibily calculated user end and off server), so you can get a rough compairson w/o having to make large SQL request.

I said it somewhere else and I'll say it again. Shoot till the base is dead. If you NEED to monitor the damage count so the base doesn't die too soon, then you're doing a disservice to your legion by targeting too weak of a base. Go to the next level.