I started the thread with '"5 iq points dumber" (whatever that means)'. I intended that to be read something like "as if there was an objective measure of intelligence that scaled like iq'.

I cannot say what other intended, but at least some people are reading this whole thread in that context and I would expect you to as well even if others didn't intend that. (that is "respond to the strongest plausible interpretation of what someone says, not a weaker one that's easier to criticize. Assume good faith." - hopefully this helps you see context better)

> talking of IQ in a quantitative way ("x points less")

I read that as a within a single individual, case A (no brain damage from cause C) vs case B (with brain damage from cause C), where using it as a shorthand for intelligence differences within a single individual makes it a useful shorthand for most readers, IMO.