Re: You don't need to know how 1,600 services work
As for the resources wasted, it really depends what they use for serdes and how much of it they do. The slide mentions RPC, so hopefully they are not wasting CPU time for number-to-text-to-number conversions. This is probably the biggest resource sink, when operating on floating-point numbers, in the architectures I know. As for the asynchronous communication over the network, if the volume is not excessively large you mostly pay in latency rather than other resources.
The nice side of a well designed microservice architecture is that you can tell which services are little used and, because each is relatively simple, you can also retire them and/or move functions elsewhere without much impact elsewhere.