In principle I agree. But OPC UA from an implementation standpoint of view is much more complicated and involved compared to modbus. I also would express your

In principle I agree. But OPC UA from an implementation standpoint of view is much more complicated and involved compared to modbus. I also would express your second paragraph slightly different. Each industry has its own preferred protocols and they are enhancing them and creating new ones. Additionally most companies offer OPC (UA) interfaces, thus making OPC the only protocol which is used over all industries. So if you want to interface with industrial systems, there is a good chance that the only thing you need is indeed OPC UA.