As someone who has been involved in a greenfield design system build for the last six months, I empathise a lot with Amy's well-worded explanation of why content design should never be overlooked.
I'd even go a stretch further, and just say that design systems can only thrive when all front-end disciplines are brought together early, and actively lean on each others speciality knowledge. Design systems can be used to scale best practices, or bad practices, equally, so best to catch things early and bake good ideas in at a foundational level.
On why content matters, and how design systems can scale little issues rapidly into big problems:
Leaving content out of the equation damages the user experience, and when we do this at the level of design systems, we’re allowing that experience to scale.
On the long term repercussions of not involving specialists early in ideation:
It means content designers have to spend time identifying and correcting widespread issues they probably would have caught at the root, had they been involved in the design of the system component or pattern.
On why consistency in language across a site is a core requirement:
Perhaps I’m biased, but I’d wager that using different words to describe the same actions, processes and information is the most damaging and confusing kind of inconsistency of all.