DSXchange

I'm not sure that they know what they're talking about either. Hashed file lookups are the fastest around.

If they're saying that your "code" needs to be optimized, ask them "what code?". You're working in a GUI environment, not a code environment.

If they're so clever, why don't they do it themselves?

What - precisely (and in English, not in a diagram) - are the two jobs intended to accomplish?

I guess, they are messing up with "Informatica" stages, and referring to the sparse lookup.
If the number of rows in the two sorce is not extremely huge, explain them that, lookup made through the hashed file is more effecient that an sparce lookup done over an indexed table.