Summarizer

That seems like it's within striking distance of competitive, no? You get some major advantages in size and production automation. Perhaps it's ok for it to die sooner if you can get it built now and then replace it later.

Standards/regulations that the transformers almost certainly don't meet, produced in factories that don't follow any standards or regulations, and then add in the cost and delay in shipping something like that.

The basic problem is easy to grasp, like the mess with charging cords for laptops before it, every large power transformer is a custom design. The fix would be to standardize on a much smaller number of options, and parallel them for the desired loads. Think of it as analogous to USB-C power, on the megawatt/gigawatt scale. ;-)

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

On a national scale, keeping a stock of transformers is peanuts. For this to be viable, they only need to be interchangeable, not identical.

It might be easier for DC transmission components to be standardized. Sure, anything with complex controls has a lot more opportunity to fail to interoperate, but DC gear can often be configured for different voltage ratios and can much more directly control how much current flows where. Maybe the grid needs a multi-source agreement for equipment like the network industry has for optics.