The reason that I think this is because it seems that all of the thinking-enhancement tech we've developed through history seems to have had that effect. They may be amplifiers society-wide (although I think that's a debatable assertion), but it's a different story individually.

> knowledge/productivity boost

That might be true, but knowledge and productivity are different things than intelligence.

Evolution follows the path of least resistance

This of course happens presently but to a smaller extent, last 4 decades at least with those attaining position that feedback loops or whatever data suggested they didn't really need to have a population educated higher than the position they might end up at, and with narratives on other agendas eg [1] pushed that much of the population just accepts that's the status quo.

[1] The most striking example I can think of, any time vegetable oil for fuel is mentioned in the news, almost without exception people will think biodiesel and the issues that might arise with certain engines. The reality is we never read much about cracking that oil into regular fuels as the industry presently does with some fractions of crude oil - I've only seen it mentioned it in one book, but it was IIRC written specifically for the petroleum industry in mind.