It's a legitimate criticism. The claimed benefit of "vector processing is faster than pointer chasing" will materialise only when the most common access pattern

It's a legitimate criticism. The claimed benefit of "vector processing is faster than pointer chasing" will materialise only when the most common access pattern is to read or write all node values, since in that case the accessed values are contiguous -- but that's a consequence of the data structure being a struct-of-arrays (instead of the more common array-of-structs), which is wholly independent of the pointers-or-indices question. For any of the (very common) other access patterns, like a preorder traversal, "index-chasing" needs to happen, and that will be exactly as bad as pointer-chasing would be if the entire memory block had been reserved ahead of time in the same way. The only real advantages of indices over pointers are serialisability and ease of debugging.