I've had four experiences with new tinplate. Two 1988 LTI Hiawathas, the standard gauge Hiawatha, and the Lionel Prewar Celebration Red Comet.
Now my first LTI Hiawatha and the standard gauge Hiawatha were fine out of the box. The second Hiawatha had a rough spot on the black. I rationalized this as being OK, if only because I paid $350 or $400 for the set, unrun, in 2005. The only issue with the red comet was that they put the smoke stack on backwards.
Whether you have personally experienced this or not, we all know that the issue is out there, and more recently, issues with die cast parts exhibiting the same metal fatigue that early prewar pieces get. This issue, in itself is unacceptable so many years after the original issue was known.
The point is that these paint quality issues have been going on for decades with MTH. But, this issue really is a double edged sword.
First of all, the new tinplate, while priced well below the cost of a decent original (or in the case of the Brute, and similar products, previously unavailable), is still quite expensive, and therefore, some inherent freedom from defect is expected, especially from adult buyer target audience.
Face it, you would not accept a new car with paint or operational defects (as best as you can tell), but, if you were 10 or 12 years old and got a new Blue Comet, State set, or Showroom cars, you would not even see the defects, you'd be ecstatic that you got them.
The second is that original tinplate was not perfect by any means. It had some seriously thick runs, crooked lettering, mismatched trim between pieces, etc. But, the difference was that these were toys , and generally not collectors' pieces. Now I know a lot of modern buyers are operators, but the trains reside in the hands of adults, not children, so there is a difference in the way they are viewed and handled.
After reading and contributing to this forum for at least three years, I noticed that there is a recurring issue with the quality of MTH tinplate, when it comes to received condition, and some operating complaints (don't know if their regular line has the same issues), all leading to a degree of buyers' remorse with the items.
MTH hasn't seemed to adequately address these issues, some of which they have had since the 1980's, and I doubt that the cost of dealing with complaints outweighs the cost savings gained by living with the statistical number of defects they get doing business the way they are.
I do not know from personal experience or from reading if there are major issues with the Lionel Prewar Celebration items or the standard gauge Hiawatha/Commodore sets, other than some fidelity issues concerning wheels, etc. Maybe since they are now working together, they could use each other's experience to increase the quality of the delivered product.