I've used Fira Code with ligatures for years now and don't find it to harm either readability or productivity, in no small part because the new ligature fonts were designed with readability in mind.
If you don't find it readable, then choose a different font, or turn off ligatures (an option when using Fira Code; I don't know about the other ligature fonts, since I don't use them).
I suspect that's highly subjective.
I've used Fira Code with ligatures for years now and don't find it to harm either readability or productivity, in no small part because the new ligature fonts were designed with readability in mind.
If you don't find it readable, then choose a different font, or turn off ligatures (an option when using Fira Code; I don't know about the other ligature fonts, since I don't use them).
I couldn't have said it better myself.