That's exactly the problem. Too much contrast is a thing with text and can make a website uncomfortable to look at (for me at least). It's hard to find a source for that, but most people seem to agree (see ~95% of other sites).
That's not a problem on commodity LCDs (maybe the one you're using) because "black" is fairly bright, but on OLED especially that's almost infinite contrast.
Therefore, instead of having your browser enforce a lowered contrast for yourself, you prefer that the majority of the rest of us, with commodity LCDs, suffer too little contrast by asking for the colors to be changed on the website.
Design websites for correct display devices, and calibrate your display devices to correct for imperfections.
Asking for users with good displays to intentionally reduce the displays' quality to simulate a bad display is just ridiculous. That's what color profiles, LUTs, and tone mapping are for.
The text should look great across most browsers/sites, and I make sure the layout flows well if you increase or decrease font size... but if you can send a screenshot of what you're seeing and your device/screen configuration, I can take a look at what might be going on.