Ethernet can be deterministic A major criticism of Ethernet for control is its supposed lack of determinism. The basic TCP version is based on probability theory, that is, the probability of collisions among packets of data on the wire can be calculated. Use of an active switch eliminates all collisions and the statistical setback that makes collision domain Ethernet nondeterministic. Switches do not even cost much these days. One of the problems encountered when discussing Ethernet is lumping various terms together under a single name.
Ethernet really describes a physical medium and data linking.
The issue goes beyond Ethernet to Internet Protocols. UDP is a simpler protocol that is much harder to use, but provides ways to improve performance on private networks. Companies marketing strategies bring on part of the confusion. In a rush to point out benefits of its strategy, a company may lead potential protocol users and automation designers to believe that the entire architecture is in a state of chaos. There really isn t any reason to limit the use of a protocol.