Yes, exactly. My point is: what is the use case where you would ever want "+01:00"? If you want to express an absolute[1] time, you use UTC or seconds since epoch. If you want to express a time that's meaningful to humans, you need a symbolic timezone (otherwise the answers to questions like "what is the time 1 day after this" will be surprising).

[1] Yes, I know there's no such thing as absolute time; perhaps "machine time" expresses what I mean.