> To measure is to quantize, so this is circular reasoning.

This is a fundamental misunderstanding. Measurement (which is a precisely defined mathematical concept) is not the same thing as quantization. For a very basic example, in all known physics theories, including QFT, SR, and GR, space and time can be measured, and they are not quantized. In fact, there is no theory compatible with SR in which space and time can be quantized, given the nature of the Lorenz transform: SR predicts continuous length contraction from the PoV of observers moving at any velocity relative to each other; for any distance of length 1, some other observer can exist for which the length would be 1/x, with x as a real number.