Theres no point making comparisons between Robles and what others have and haven't done before him. There's no hard and fast way to the top, just look at what Seamus went through before he arrived here aged 22 and what's happened to him since.
What matters is what's happening here and now. Robles is performing as well as the other top 6 keepers and has been for a number of months. They all make saves and they all make mistakes we naturally scrutinise our own more.