A quick read of any old usenet arguments should instantly disabuse you of this absurd notion. Or the old archives of stupid IRC conversations.
The old internet was a space for people who were incentivized to spend significant effort dealing with technical things to connect to strangers, which has nothing to do with IQ or "intelligence" or anything like that.
There has always been plenty of people who are extremely stupid, but have no problem following technical minutia as required for things like the early internet.
Remember that early access was extremely expensive. Usually it was billed hourly, at significant rates. This means that the primary filter for internet users back then was connection to resources, through an academic connection, a corporate connection, a government connection, or a lot of personal wealth.
The quality of internet users early on, if it even existed (which I dispute), was more driven by organizations like the government, academia, and defense contractors.
And as much as people cried about "Eternal September", the internet mostly survived as a distributed place with real communities until the late 2000s, where it started to be really profitable to build walled gardens for Advertising economies.
The walls didn't really come up until the 2010s: Facebook being a dominant platform, Google owning Youtube and leveraging that to try and force their own social network, Apple controlling most phones, old forums dying, and the rise of AWS to centralize internet software design.