At NTSC timings, 80 column text is basically color information. It's just terrible.

Interestingly, sets from about the 80's onward can display 80 column text nicely, given a good DAC driven signal. The signals from back then were square, or coarse, if not square. This makes NTSC light right up. I've been toying with a micro and a DAC and a full interlace, color phase shifting NTSC signal performs well on older analog sets. If the timing is right for the digital ones, they do well too, but it's all about hitting that 13.5Mhz sample window common to most digital sets today.

Back then, just having a full interlaced signal would have helped considerably with text, though at the expense of tearing. Low ambient light and moderate contrast on the display would have largely mitigated this.

As we got Y-C capable displays, one could just use a resistor and send the composite signal into both inputs. This actually did very seriously improve text.

Part of the reason for this is that IBM split the market into CGA for graphics and MDA for better text (9x14 character cell). Because the MDA adapter didn't display graphics, IBM made it possible to run both a CGA and a MDA in the same machine. Software like Lotus 1-2-3 could put the spreadsheet on the MDA and the graphics on the CGA. Dual monitors in the mid-80's.

Prior to the development of the EGA and VGA, there were a few interesting competitive responses to IBM's CGA/MDA split. The first was the Hercules card. This would let customers that had bought IBM's MDA (and it's matching monitor) get access to graphics. It wasn't compatible with CGA graphics, but it was higher resolution and wound up being fairly widely supported where it mattered. Compaq also had a solution to the problem... they shipped adapter/monitor pairs that could display MDA-quality text in the text modes and would scale down to 640x200 to display graphics.

What ultimately wound up happening is pretty much what you'd expect. As graphics resolutions got better with EGA and VGA, the quality of text on color displays got to the point where the MDA didn't represent an improvement. That said, there was always the ability to run an MDA (or clone) in parallel with a EGA, VGA, etc... that configuration was useful to programmers because it let you put debug information on one display while the main display ran the software you were developing.