Duke, I wouldn’t call this the idiots way, I would call this the smart way.
There is very little need to “work” at 4k. I routinely set my timeline to HD, do my work, then switch it back to 4k for the final renders. If you are pulling keys that require the 4k source, then switch over, but I would suggest 95+ percent of your color work can be done in hd with a final switch to 4k prior to render. Even outputting client approvals can usually be HD. In fact my last 4 projects were shot at either 4k or 2.8k, and didn’t see the source resolution until final render, except for the day of VFX plate outputs, where the timeline was set to full res.
I have a preset ready to go for 4k, 2.8k and HD and it takes about 5 seconds to switch from 1 to the other.
And yes, you do need to set your timeline resolution to 4k prior to rendering, otherwise you are upconverting from your timeline resolution to your output resolution.
As for your black bars issue, you need to look into the image scaling settings and play with the scale with crop vs scale to fill screen vs force all the corners settings. In there you will find your ability to get rid of the letterbox, while maintaining aspect ratios.
Glenn