If a personal account is of any use...
I've recently been re-introduced to the 16 bit computing world on buying a Philips monitor off eBay for my Atari ST ... which happened to come with an Amiga 600 and a large bundle of software
The Miggy's computer-to-monitor cable was actually damaged, leading to the interesting quirk where the screen that came with the machine could then only be used with its older rival. But, no matter - unlike the ST, the A600 has 3x RCA composite/stereo output built in!
And I must say it actually works quite well. This Amiga, after all, has modes from 320x200 going up to 1440x576 on a standard-definition monitor (and a couple VGA ones if you hook up a multiscan). The very highest ones still displayed on both the CRT and LCD televisions I connected it up to, but weren't exactly usable. You'd need a special reason for trying to use a 1280 or 1440 pixel wide mode for anything on a standard def TV. I can only assume that, given how it also had a rather slow update and very limited colour depth - 4 colours from 64 instead of 64 from 4096 - it was meant for very detailed "serious" work on a monochrome (and therefore effectively "infinite" horizontal resolution) screen with an anamorphic lens in front of it as a cheap substitute for a proper hi-rez monitor...
However, the lower modes look just fine. 320x200 thru 360x288 for gaming are perfectly crisp and clear. 640x200 thru 720x288 are good for regular productivity uses on my old 14" CRTs, no problem reading the text at all. It's not quite pixel-sharp, especially on the one that's actually a salvaged CCTV monitor (makes little difference in this day and age, both monitors and analogue TVs need a freeview box) which only appears to have about a ~450 pixel physical horizontal resolution, but you don't have any trouble making out what each letter is with a standard 8x8 font.
Better yet, 640x400 thru 720x576 look just spiffy on the LCD - it basically has a built in "flicker fixer" in order to upscale interlaced material to full screen progressive, after all. Interlace mode still works on the CRT, but it's kind of hard on the eyes because of how any single-height horizontal line (including lines that are part of letterforms) flickers at 25Hz instead of the just-about-tolerable 50. On the LCD, it's steady, smooth and readable, with just a little shimmer around any moving objects. I think the screen doesn't have a quite large enough screen buffer (probably has 1mb? which means with a typical 18-bit LCD colour depth, you can only fit 704x576 not 720x576), so there is a little bit of uneven-looking horizontal resampling in 80-column mode, but it's not too bad. ((NB this happens even with smaller resolutions in the same actual "mode", as the Amiga achieves, say, 640x512 by simply limiting the active screen area to the central 88% of the actual generated signal, and the rest of it is a blank "overscan" border that would normally disappear off the side of a TV - my CRT can actually manage about 680x540 maximum)).
There's also a little bit of horizontal colour smear around finer objects, but it doesn't affect the *monochrome* clarity. A pure primary colour on black, secondary colour on white, or one colour on another will give a fuzzier result (40-character is about your absolute limit for any kind of readability), but secondaries on black, primaries on white, and most particularly black/grey/white combinations are nice and clear.
All in all you can get a very nice output for word processing (actually tested!), programming, using the console (I totally don't understand AmigaDOS even after reading the manual several times, it's just weird), a nice high-contrast GUI (workbench themed et al) and the like in 80-90 columns over a decent composite output with a moderately recent (last 20 years?) TV. With 25-32 lines on an interlaced CRT, and at least 48 lines on even the cheapest, nastiest, smallest standard-def LCD.
Wouldn't recommend 6x6 font for anything but all-caps labels, though. Like the Atari used for disk and file icon names
I've also run PCs via converters from 640x480 up to 848x600 (and, with internal downconversion, 1024x768), which worked with varying degrees of over/underscan and readability. I still found the best results were to be had by getting an advanced-level driver (either OEM or third party tool) which let you tweak the exact resolution and timings, setting the equivalent of a standard 720x576x50 overscan screen (something like 768 x 625 actual lines... the interlacing was done separately, at least, so you could set it to 50p with 625 lines) for the actual signal timing, and then defining a custom resolution within that frame to nicely fill the display without losing anything important in the corners, say 688x528 (you can usually guess that the extreme edges of a windows screen with a maximised program are going to be, clockwise from top left, Window Menu, Close Box, Clock, and Start Menu).
Question is, what resolution does the Pi default to, especially on composite if it can autodetect what output is being used? And does it have any kind of built in de-flickering filter? IE something that will blur slightly between the individual lines of a full rez interlaced screen? If it's 640x480 with a moderate filter, preferably a software switchable one (ie it can be turned off for use with an LCD TV) we're good to go for basic use. If it's higher with either an overly aggressive filter or none at all, that makes things a bit more difficult.
(Incidentally, in terms of filters, back when I was manually making VCD and then DVD menu images from scratch, I found you could get a very good illusion, on a CRT, of full vertical resolution with minimal or no flicker on the text and finer details by pre-filtering the image; basically I applied a one-pixel vertical motion blur to the whole thing after finalising the look and the layout, then did a couple test runs to determine whether it looked best with no filter, full filter, or an image that merged 50% between the two. Usually one of the latter tended to win, depending on actual contrast and text size, so something like a 50 to 75% vertical softening filter might work well if you had to choose a single "strength" setting. Often it would allow somewhat smaller, readable detail text than could be displayed either unfiltered or in a 240/288-line mode, as well as a finer-lined font or more striking high contrast outline/shadow effects for the titles, without producing horrific flicker. Of course, it had no effect on the horizontal resolution...)
Hope that's maybe of some help or guidance!