This is only if the 1000 children are already in memory. Otherwise it is still 1000 lookups, by index. This is why the Graph Dbs on the market tend to be in memory.

I'm not saying Graph DBs don't have their place. They do, but they are the wrong answer for MOST datasets.

NO. Each lookup thereafter is NOT by index. That's where the savings come from. The pointers already contain the exact block where to load the info from.