I disagree with your using "intended for use by one person" as a key defining point of PC. The revolution of the PC was that the physical size had come down enough to where it was plausible to have one in a personal space such as a home, opposed to a space such as a business or university, and did not need to connect to a mainframe to function. Much like the early days of the TV, you would have one per household, not one per person.
The phrase you need to be concluding on is "general purpose computer". Tablets and Smartphones are, by design, NOT general purpose computers. The companies making and selling them do not want you to use them as you would use a PC. They want you to consume media, which they can charge you more money for, and then share that media with others so that they can in turn charge them as well.
PC is not redefined based on how people use their PC. Just because the majority of the people today who own a PC only use it for browsing webpages, listening to music, and watching video does not mean that any device that can do these things is now a PC.