[quote=@Havoccultist]
[@Sep]
...Depending on how powerful the fleet's lasers are, they can only core through so much of the city's layers before hitting a depth they can't penetrate. Especially if you factor in diffusion as the projectiles travel and whatnot....
[/quote]

Covies actually have a way around this! Covenant energy projectors utilize gravitic impellors and gravitational lensing to focus their beams to an extremely precise degree, though these aren't lasers.