How a large number of IP addresses are wasted using IPv4 address classes?

If a network has slightly more number of hosts than a particular class, then it needs either two IP addresses of that class or the next class of IP address. For example, let use say a network has 300 hosts, this network needs either a single class B IP address or two class C IP addresses. If class B address is allocated to this network, as the number of hosts that can be defined in a class B network is (2^16 - 2), a large number of host IP addresses are wasted. If two class C IP addresses are allocated, as the number of networks that can be defined using a class C address is only (2^21), the number of available class C networks will quickly exhaust. Because of the above two reasons, a lot of IP addresses are wasted and also the available IP address space is rapidly reduced.