Copying from what I said in a different thread
Seriously? The laser turrets literally outdamage every other turret on the map and do more damage then the old base turrets ever did. They have stacking armor pen (up to 75%) and massive damage. For math, laser turrets max out at 290 AD (~43:00 minutes when they max) compared to 250 for the inner turrets, 4.0 AS compared to .83, and 75% armor pen compared to 30%. Their stacking counter is weaker than other turrets (ramping up to 125% after 5 seconds compared to ramping up to 225% after 4.82 seconds), but when taken with their AD and per hit their damage is MUCh higher. A max heat laser turret does 2610 damage a second; a max heat inner turret does 674.38.
Also, this is a tower defence game, not a tower defence game. The turrets aren't there to protect you lategame, they are there to clear minion waves and provide a boost if a fight breaks out under them. A turret early game protects you from being dived and is comparable to a champion in terms of help. A turret midgame is there to deter dives and help clear waves and put some damage on enemies. A turret lategame is there to clear waves and SLIGHTLY deter enemies. League is about the champions fighting; the turrets aren't there to do anything except keep minions out and protect you earlygame.