Haven't read the whole thread, but I'd say eliminating time zones causes an issue when needing to know what time of day it is in another place. For example, if I were in London at 13:00 then with time zones I might ask "What time is it in Singapore?" and be told it is 21:00. We're naturally tuned in to understand what happens at different times of day so the time difference/zone is inherently useful.

If we had no time zones and I asked the same question then the answer would be 13:00, but it doesn't help me know whether someone might be asleep, at work, or able to take my call so we would still need to know the time offset.