A modern data platform is not a newer version of the one you have
Modernization
The systems running most industrial operations were built to store readings and draw charts. They do that well. What they were never asked to do is explain what a reading means, and that is the part everything now depends on.
Three things are different now, and only one of them is technology
The questions stopped being known in advance
A historian is built around the reports someone specified when it was installed. Every question after that is a project. A modern platform holds the model of the operation instead, so a question nobody anticipated is answered from what is already there.
Software became a reader
A chart is read by someone who already knows what a tag name means. An AI agent does not know, and will fill the gap confidently. Modern means the meaning is stored beside the measurement rather than carried in the heads of whoever has been there longest.
Storage stopped being the constraint
Keeping ten years of second-level history used to be a budget argument. With columnar storage and the compression it allows, it is a decision you make once. What costs money now is modeling, not disks.
Most of it is not replacing anything
Your control systems are not the problem and should not be touched. Neither, usually, is your historian: it is a good archive and it can stay one. What is missing sits above them, the layer that says what an asset is and how the measurements relate to it. Adding that is a smaller job than a migration, and it can be undone, which a migration cannot.
Not sure which part of this you already have?
Tell us what your operation runs on today and what you have been asked to answer with it. We will say honestly whether the gap is a platform or something smaller.