I love battle reports so much!
I like to think of Custodes as mini-Knights. They are so tough and sometimes you don't have anything that can really wound them... but they also have so few models that you can potentially outscore them because they simply don't have enough models or models that can cover enough distance to score well.
You are 100% correct.
I treat them like tanks and fire Lascannon at them.
I know they have a 4+ invul but I make them sweat every time I wound them and when some go through, D6+1 damage basically sees dead Custodes happen most of the time!