I think the usual issue is a mirrored surface is not robust enough to absorb extreme levels of energy for very long before it becomes a poor mirror. I expect t

I think the usual issue is a mirrored surface is not robust enough to absorb extreme levels of energy for very long before it becomes a poor mirror. I expect the counter will be more along the lines of having sufficient ablating material to block the laser - a small amount of extra armour probably has an outsize affect on survivability.