Whether the problem is serious enough to be worth fixing is up to the individual. I saw an article about this kit in FSM a month or two back; I frankly thought the finished model looked pretty good. I think I probably would have noticed the inaccuracy of the surface detail if it hadn't been discussed in the forum, but I'm not sure it would have jumped out at me.
In trying to explain it I need to repeat one big caveat: I don't have the kit. (It's our of my price range - at least for this sort of model.) I'm writing on the basis of photos, and of what other forum participants who have bought it have said.
The basic problem apparently is that Hasegawa covered the surface of the hull with a rectangular grid of countersunk lines, some of which are in the right places but most of which aren't. The impression is that the hull is made up of hundreds of plates with grooves between them. The real thing isn't. (I don't know how many plates actually made up the hull of a Nagato-class battleship, but I suspect it was in the scores - not the hundreds.) Most of the countersunk lines don't accurately represent the edges of plates, but rather ink lines on the plans that were drawn to establish the cross-sections of the hull. A twentieth-century warship simply doesn't have an enormous rectangular grid of regularly-spaced vertical and horizontal lines etched into the surface of its hull.
In a real warship of that period there would indeed be both vertical and horizontal seams between plates, but they wouldn't have grooves between them. They'd be riveted or, more likely, welded together; in the latter case there would be a barely-visible raised line at the joint. In most cases (not all) the plates would in fact overlap slightly at the edges. (Ship enthusiasts talk about "inners" and "outers" - plates that overlap or are overlapped by their neighbors.) In some photos the difference is pretty conspicuous; in others it's unnoticeable. (The big difference usually is the angle of the light.)
So, to boil it down to the simplest terms, there are far too many lines and they shouldn't be countersunk.
I'm reminded of a 1/72-scale DC-3 / C-47 kit that one company (it was either Italeri or Esci; I don't remember which) issued back in the 1970s. The designers apparently had worked from a set of plans that showed all the frames and stringers of the fuselage - and assumed all those lines were the edges of panels. So the kit had a complex grid of countersunk lines all over its fuselage. Only a few of those lines actually indicated the edges of panels; the others should have been lines of rivets.
Again, I'm not suggesting that this "has" to be fixed. I'm just suggesting that anybody shelling out the huge amount of money that this kit costs is entitled to know about the problem and make his own decision about it.
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