With 1 satellite and 1 main unit, the bandwidth loss isn't as bad since Orbi uses a separate radio for backhaul. Cheaper mesh systems use the same radio for backhaul and you lose alot of bandwith from the 2 way communication, since the same radio has to receive it, then transmit it back out.
With multiple satellites in a mesh system, bottlenecks can come when multiple satellites and clients are trying to hit the same node. So lets say you had 2 satellites, but the far satellite must communicate with the middle satellite to connect to he main router, since it can't make a direct connection due to distance. Several clients are hitting the far satellite because they live on the end of the house. Then you have 1 person connected to middle satellite trying to do a game console update. Well, everyone on the far satellite and the middle satellite would grind to a halt because all traffic has to go through that single backhaul channel. That's why mesh systems are frowned upon by most people. If you can avoid them and do some type of wired backahul to the main router, such as coax or powerline if you can. Wifi repeaters and mesh systems should be considered a last resort, unless all you have are people that just surf the internet an watch netflix. If you have any high bandwidth users, the system can grind to a halt.