I've got a ton of old tech and it's hit or miss about how composite video is going to look... not all output is created equal.
The Retotink helps, but even as such I think the monitor itself makes a big diffrence... most of the manufacturers don't seem to have put in a whole lot of effort in the upscale od the old standard. I've got two other TV's and a couple other composite to VGA and HDMI converters to try. I haven't had a need yet for retrotink's Rpi to RGB converter... and it not cheap.
I've got a couple other ideas on how to clean up composite video, I've got one peice to equipment to try, and I'm trying to get ahold a couple other versions..