Was "Cuán(to)..." always synonymous with "Qué tan(to)..."?

Question

In many dialects of Latin American Spanish Qué tan(to)... is used in interrogative/exclamative phrases with the same meaning as the Cuán(to)... (or Cómo de...).

Indeed, this phrase was used in Spain with some frequency up until the 17th century.

Question: Was cuán(to) always used in this context in Spanish, alongside qué tan(to), or did it only acquire this use later on as qué tan(to) was declining in popularity in Spain?

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<sup>1. DAMER: tanto I.e) ǁ ¿qué ~?
2. DLE: tanto qué tan, o qué tanto
3. DPD: qué 4.(g) qué tan(to).</sup>

Answer 1

I cannot fully endorse that its popularity has been declining; however, I can confirm that they can be used interchangeably.

Although, I prefer using ¿Cuánto... to ¿Qué tanto.... depending on the case. Namely, I would say,

—¿Cuánto dinero necesitas?
—¿Cuánto la amas?
—¿Cuánto tiempo estuviste ahí?

but I wouldn't replace cuánto by qué tanto in these cases. And yet, its use hinges profoundly upon the region you are, meaning that it may sound idiomatic for some, but not for others.