My response to "Oh, I can implement this in 5 minutes" is always "but will you support it?"

I think this is the hardest thing about moving from a startup to a more mature company (either through growth and age or acquisition); you have to move your mindset from building to supporting. Building is fun and creative, supporting can be tedious and soul sucking (but needed!). It's a huge, and legitimate, reason why large companies slow down (either to support, or to consider support in the build process).