In my experience, making the ratlines ahead of installation does not work. One thing is indiputable- that method cannot be accurate.
In general, on a ship, it goes like this.
The foremost shroud on one side runs up to the top. It passes up through the opening in the top, is passed around the mast over the trees from front to rear, and is returned back on the same side of the ship, down to the tightening assembly (lanyards and deadeyes). At the mast, the two runs are seized together.
The process is next repeated from the other side. That shroud lays on top of the previous one.
Back and forth. If the ship has an uneven number of shrouds on each side, the rearmost does go up one side and down the other, but only then.
What you end up with is a big stack of shrouds wrapped around the mast, from left and right. Often that stack is about as tall as the mast head cap itself.
On a larger scale model, this kind of stuff matters. There is absolutely no way that a preassembled shroud and ratline assembly can be made to do this. And as far as I can see it's no less effort to assemble the thing on a "loom" than it would be to do so in place.
One perfectly acceptable solution, IMO, is to set up all of the shrouds, and leave it at that.
Ratlines can be added later, although it gets harder the more of the rigging is installed around it.
I hope that's helpful.