Earlier quoted context omitted.
The inscriptions were very obviously not done in the same physical culture as produced the boxes. The boxes are marvels that could not be produced even by the best modern stonecraft methods. The inscriptions are crude hammerings; one might equally-well equate genetic engineering with tattooing. Nobody knows how old the boxes are, or the tunnels they are in. All that is clear is that later people used the site.
I don't find your conclusion obvious. Yes, the construction seems better than older Egyptian examples. But that makes sense: the later date of construction in the Iron Age means more ubiquitous iron tools. The inscriptions don't seem crude to me. Better than the Rosetta Stone. Worse than the Stele of Thonis-Heracleion. In short: You don't give Saite-period stonemasons enough credit. But this is a digression. You want…
The Rosetta Stone's uneven lines are markedly better-made than the crude inscriptions lately applied to the Saqqara boxes.
The quality and precision of stonework seen in the boxes at Saqqara most resembles that of the best archaic and pre-dynastic jars.