Yes, but they can be flooded as well. Every system is going to have a finite capacity. And if the capacity is exceeded, the system will slow. If the capacity is significantly exceeded, it will become unreachable itself.

So if the capacity of your system is X Gbps, then it will start to have problems if the attacker sends X + 1 Gbps. And will probably be completely unreachable if the attacker sends X * 2 Gbps.