No, I am not, at least insofar as I am presenting some of what I perceive to be historical background. There is also a vocal contingent of folks who would call you and me heretic for suggesting that tailoring for level-appropriateness is allowed in "real" sandbox play.
I don't think those folks represent a mainstream opinion. Historically, I believe the term arose as a retronym to describe something that was dissimilar to the usual "JRPG" format and became a tabletop RPG term sometime in the early Internet era. It originally referred to the playing environment, not to a resolution system, and I think it remains clearly only if it is used in that way.
Obviously, terms change over time, but suggesting that sandbox, therefore status quo, doesn't seem to add anything and it does suggest several logical contradictions in the idea of a status quo encounter. First, imagine you are playing Fantasy Craft. If you try to set up status quo encounters, you will quickly discover they scale, to a great extent, based on PC power. On the other hand, imagine you set up a world in which more distant opponents exist and are training... if the PCs meet them later rather than sooner, the NPCs will be corrrespondingly more powerful. Is that status quo or tailored? On the other hand, the logical problems evaporate immediately if you take status quo/tailored to mean literally whether you adjust the encounters to match the PCs. Instantly, we see that Fantasy Craft encounters are primarly tailored, and in the second case, it depends on whether that training is mechanistic or defined in some metagame respect based on PC ability.
"I can go here, I can go there, I can do anything" does not assume anything about how encounters are resolved. A Cr 18 dragon presupposes a level-based system with tiered monsters; no such thing exists in Fantasy Craft. Although we might imagine a dragon as having CR 18 statistics, in fact, that whole system is an artifact of a particular combat resolution system and experience system. If you replaced d20 with "d02," you would have the same dragon, but the PC would have an even chance of winning, regardless of when and where they met the dragon.
I'm not crazy about the term "linear"... I usually say
programmatic to mean the GM prefers a certain series of encounters.