First of all, it's not a straw man. Spellcheckers were standalone applications for years before word processors began integrating them. [1]

And second, it's not a slippery slope fallacy, it's an actual slippery slope, that's the whole point. There isn't a "pretty clear distinction" at all.

If I understand you correctly, you're arguing that when spellcheckers came out, the existing products should have been able to legally prevent WordPerfect (and eventually Word, and Docs, etc.) from ever building their own integrated spellcheckers. To this day, you'd need to buy Word, and then buy a separate spellchecking app or extension.

But there's no distinction between spellchecking and 100 other features that Word has that also used to be separate programs -- like mail merge, like drawing capabilities, like a citations manager, etc. etc. etc.

And you really think that would be a good idea?

[1] https://en.wikipedia.org/wiki/Spell_checker#History

I'm not seeing a clear distinction. Imagine a scenario where Word and Excel aren't bundled. Word has always had table functionality. The Word team decides that it'd be useful if, when creating a table, end user is able to enter @cell1 + 1 to cell two to make it show the incremental value of cell one. Soon enough they'll add sort, sum, average. Then they'll create a template that creates a document with a table created by default, which looks like a spreadsheet.

Should those new functionality be allowed and who get to decide? Any attempt to regulate such product features are futile and inevitably stifle innovation.

Apple M1 is universally praised exactly because it's a SOC with integrated functions that used to require dedicated chips from multiple vendors. Imagine the inferior product if Apple is legally obliged to use Intel/AMD graphic card, in the name of maintaining the competitive landscape?