My point is we have that unambiguous system you want. People don't use it except in specific circumstances. Instead of saying those people are wrong, you can look at why they don't use UTC for everything.

People don't use UTC because people aren't usually interested in universal time, they're interested in time of day, which is fundamentally tied to the position of the sun and people's day night cycles.
The people in China who made their own bootleg timezone illustrate that perfectly.

We don't currently have to reason about where someone is physically located to know if they're likely asleep. I'm in UTC-4. It's 15:30. It's 19:30 in London. I know the evening is advanced enough that I shouldn't call my coworker there, but early enough that I can if it's an emergency. I forgot California's timezone, so I googled it, and it's UTC-7, so it's 12:30 there. I should probably wait half an hour to call to avoid the typical lunch hour.
Otherwise I use a tool to look up and see that solar noon in California is around 20:00, so people are probably doing their midday routines then. Except that California shifted business hours so that they're offset an hour from solar noon to reduce energy consumption, which I didn't know.
And what do we do about places like Texas where solar noon varies by more than an hour on different ends of the state? For simplicity, most regions like to synchronize working hours inside their contiguous economic sphere. So I can assume that the state would pass a law relating to what time was considered "convention", since we need schools, businesses, banks and government services to be consistent inside a jurisdiction.
It's important we have stuff like that be uniform, because jurisdictions have laws about stuff like preventing teens from working during school hours, or preventing schools from starting class so early it interferes with children's sleep or staying in session so long it interferes with their evenings.
Texas can just mandate that standard business hours are 14:00 to 22:00.
Thank God they didn't end up having to mandate that the standard business day is split across two different calendar days like California. Imagine the hell of child labor laws when you have to stipulate that teens can't work between the hours of 15:00 and 1:00 the next day unless said scheduled interval begins on a weekend.
Business hours being posted as 00:00 - 03:00, 17:00-00:00 for things like Sandwich shops is my favorite though. "I closed for the night today at 3, but I'll be open again later today in the morning at 17" just has a delightfully complicated inhuman ring to it.

There's a reason people like their days to line up with their days, and we like to base our clocks around how we live our lives where we are, not where the sun in in Greenwich.

I fundamentally disagree that a system that's identical to how we work with timezones but non-standard, like a UTC offset system you describe, is simpler than timezones, which are standardized UTC offsets. At best it's timezones with a different name and more of them.

Latin1 is far simpler than Unicode, and doesn't have conversion issues. It's static and very difficult to get wrong. It's clearly a better match for comparison to UTC-only. It's only downside is that it leaves everyone outside of a small segment of the worlds population to build their own janky system for dealing with their silly human need to reason about time in an intuitive sense/write their names.