A depressing number of design systems treat type as a token list — a scale, a couple of weights, done. The scale is the easy part. What matters is what the scale is for.
Measure before size
The single most consequential number in a text-heavy page is the measure: how many characters fit on a line. Somewhere between 45 and 75 is comfortable. Above 90 the eye loses its place returning to the left edge, and readers stop finishing paragraphs without ever knowing why.
You cannot fix a bad measure with a better colour.
Hierarchy is a promise
Every distinct size on a page is a claim that this thing is a different kind of thing. Six sizes means six claims, and most pages cannot honestly support more than four. When we cut a scale down, the page usually reads as more designed, not less.
The accent has a job
We allow ourselves one serif, and it does exactly four things: ledes, pull quotes, captions and statistics. It is never a heading and never body copy. The constraint is the point — a face that appears everywhere stops meaning anything.
Test it at the worst size
Set the browser to 200% and read a paragraph. Then set it to the smallest phone you support. If the hierarchy survives both, it is real hierarchy. If it only works at one width, it was a layout that happened to look like hierarchy.
You cannot fix a bad measure with a better colour.