It all depends on the underlying technology. Yes, an indirection costs more. But in the same time, the first level array can be much smaller and it even can be

It all depends on the underlying technology. Yes, an indirection costs more. But in the same time, the first level array can be much smaller and it even can be that both arrays together are smaller than the old array before, because it had to had gaps. The new compact array does not need to have gaps. It of course depends on many factors, like how is the filling factor. But, preserving memory can potentially also preserve transfers between processor and main memory. In old processors, pure clock cycles and the complexity of the opcodes where the main factor when it came to speed. Today, the complexity of opcodes (for example indirection) are less and less interesting. The amount of cache misses and how much memory must be transferred between processor and memory chips are deciding.