Boo hoo, you have to walk a little bit. Let me buy you a Segway and a reservation on the Buy 'n' Large Axiom.
Hundreds of thousands again, huh? There are 18 servers. Let's say hypothetically this game gets popular to the point that there are a million people playing. That still divides out to between 50,000 and 60,000 people per server. Not exactly hundreds of thousands.
Your retainer (and any NPCs targeted by an item search) are given a higher spawn priority. You will not only see them from a greater distance, but they are clearly discernible from the rest due to your retainer's name display being a different color, and the star icon above the heads of searched out NPCs. Not very difficult unless something's wrong with your eyes.
So?