It's a real problem but your framing of it is itself very alarming.

Most humans aren't useless by any measure of most or usefulness. Our culture is our tools, dying due to a lack of antibiotics doesn't mean you didn't have anything to contribute, it means you didn't have access to the tool you needed. This is the problem we need to guard against.

No one is going to lose the ability to reason! This is accepting the most extreme version of the marketing presented by frontier labs, don't do it. People may lose fluency or familiarity or access to training on specific skills. We should put some care into making sure that can't be a catastrophe, for sure.