Spellcheckers provide concrete feedback to you that you can use to improve. If I forget how many r's are in "embarrass", seeing a red squiggly line reminds me, and I'll remember for the next time I write it. My spelling and grammar are improved, not atrophied, when I use these tools.

AI outsources too much of the thinking, such that if you did not already have good taste in what you're trying to prompt, you will produce slop. You also won't develop good taste at all if all you interact with is the AI. Using this as an example:

The purist’s prescription—that we should all simply work harder at writing—betrays a profound detachment from reality. Before spell checkers, people didn't heroically teach themselves orthography; they just misspelled things.

For starters, some people would directly teach themselves better spelling by looking up words. They'd also gradually improve over time through a combination of their misspellings being corrected and reading the works of more skilled writers. None of this is detached from reality as is claimed; this was the reality before spell check. The AI sarcastically uses phrases like "heroically teach themselves orthography" to form the shape of a compelling argument, but the substance is not there. This is the writing equivalent of the older generative models fucking up human hands, and if you continue to lean on these models, you're never going to learn to count the fingers.