Summarizer

I worked in a machine shop of a large shipyard and 20 years ago they had CNC Winders for rebuilding armatures for Navy ships. They replaced older versions that were NC winders. So this "hand wound" story is just that. Windings going into Oil Tank? I think you mean varnish tank... After the rotating assembly is balanced they go into a protective coating tank that is a varnish.

Afaik utility scale Transformers operate in cooling tanks. Maybe that's what they meant about "afterward" "oil" covers many things. I believe the constant cycling and thermal load can make heinous PCBs.

People already parallel transformers. That's nothing new but it's usually undesirable because the extra ancillary equipment costs make paralleling more expensive than having a single transformer of equivalent rating if you are building it all at once. But even fairly small standard specification distribution transformers are custom designs or very short runs. It's not economical to make the same design year after year because the relative prices of copper and core steel vary over time. A design made last year can be uneconomical to make this year because last year copper was relatively cheap so the designer used a lighter core and more copper to achieve the required efficiency. But if this year the copper price has gone up while the core steel price has gone down it would cost more to make the same design while the same specification could be achieved for a lower material cost by making a new design. The new design is not a new type and for distribution transformers the effort required to design it is of the order of a man hour or two, far less than the difference in material costs. For very large transformers (megavolt HVDC for instance) the situation is somewhat different and the design can take a very long time. But the opportunities for standardisation are relatively small because the quantity of units in the market is small and the manufacturers and regulators are always chasing ever greater efficiencies. A far as specifications go there is already quite a lot of standardisation. But standards evolve over time and transformers can last for over half a century so you inevitably end up with a mixture of device types Also, if one of your paralleled large power transformers fails you can't just buy an off the shelf replacement because no one keeps a stock of items that cost a million dollars each. Switching to USB-C was trivial because most of the devices involved are essentially consumables with lifetimes measured in handfuls of years ad often much less so the old stuff withers away rapidly. That is not the case with large capital projects such as national electrical networks