Overturning Marbury would turn the Supreme Court into a court of review, meaning they only apply the law as written.

This is correct as to what SCOTUS can pass final judgement upon. What would be unaffected would be theirs powers in equity, which show up prominently when it comes to preliminary injunctions. So in a world without Marbury, a lawsuit against the federal government challenging the constitutionality of a particular law could not proceed, because SCOTUS (and by extension, all inferior federal courts) wouldn’t be able to rule on that question.

But if instead, a lawsuit challenges whether the federal government followed the procedures defined in law, or if there is ambiguity as to how the law might be interpreted, then SCOTUS would still have the power to intervene while the case progresses – which would typically restore the status quo, but the current SCOTUS seems allergic to that – and then could pass judgement in law on how a statute is read, or in equity on how ambiguity is resolved. Litigants would change their tactics to adapt to this environment.

This is part for core, raw power that the court retains, even without Marbury: it can, at great reputational cost, read a statute that says “no parking on Tuesday” to mean any of: 1) no parking on any Tuesday of any week, 2) no parking on only the Tuesday following the passage of the statute, and then parking is always permitted thereafter, 3) parking of automobiles is banned nationwide, but only in National Parks because of their “uniquely structured, quasi-private entity with a distinct historical tradition”, even when this openly contradicts history.

The power to say what words mean is awe-inducing but also terrifying, one that can maintain good governance but can also turn into an Orwellian double-plus bad nightmare.