But... We have UTC already, so calculating the difference is a non-issue. If you got rid of timezones, you'd still end up creating it in all but name since the vast majority of business will be occurring during daytime hours around the world. For example, an office in Tokyo sending emails to their NYC office at 0800 UTC (currently 0400 EDT in NYC) wouldn't end up getting answered for at least 3-4 hours when those employees started logging in. In other words, people would still be doing calculations in their heads to know when business hours are in that region, essentially recreating timezones.

As for your second paragraph, I agree, and I did have it backwards, thanks for the correction. In the summertime where I live, the sun has risen by roughly 0530 and sets around 2100. In the wintertime, the sun is rising around 0700-0730 and setting around 1630-1700 at its shortest daylight hours. Like you said, staying at standard would mean in the summertime we'd have brighter mornings, but curtains and shutters exist for a reason. Personally, I think having it still be bright out at 2030 is kind of annoying.