I go back to my original point, Tesla broke ground on the GigaFactory in 2013 and just hit production stride this year. That's 5 years.
Tesla was plowing new ground and doesn't have the money of the big players, but at best a big player who was willing to go for broke might be able to cut the breaking ground to full production of a GigaFactory to about 3 years. By 2021 Tesla will likely have the Shanghai plant close to producing cells and GF1 will likely be producing more than it is now.
This is almost 2019 and if Jaguar, VW, and Mercedes were going to be competitive with Tesla's volumes in 2018 by 2021, they should not only have compelling designs rolling out, they should be well along on battery projects as big as GF1. Ground has been broken on some large battery factories around the world, but most of the largest are targeting domestic Chinese production. The "Tesla killers" aren't doing much to compete with Tesla in volume.
VW has signed a contract for $48 billion in batteries, but the only year given in the press release is 2025. They are still talking about building their own factory. According to Electrek they were in negotiations with contractors a couple of months ago
VW is reportedly going to build its own battery cell gigafactory
It doesn't sound like VW Group is going to be able to produce 500K cars a year by 2021. Tesla will likely be producing closer to 1 million a year by then.
Jaguar signed a contract for 5 GWH of cells, which sounds big until you realize that's enough for 55K iPace
Jaguar reportedly signs important 5 GWh cylindrical battery contract with Samsung for upcoming EVs
Tesla makes 3 cars, two of them get more than 300 miles range for the longest range model and the third falls just shy of 300 miles.
In 2018 long range EVs need at least 200 miles of range to be considered competitive, being able to offer a car with at least 300 is going to be considered necessary soon, and Tesla is the only one who can.
The EPA has only tested one of the new European cars (the iPace), but it's numbers do not stack up to the Model X 75D very well:
Compare Side-by-Side
The iPace's energy efficiency is worse than some hybrids. It has a pack closer in size to the Model X 100D, but has less range than the 75D.
If other manufacturers will producing fewer long range EVs combined than Tesla's 2021 production (battery quantities) and can't compete with Tesla on range, and may or may not compete with Tesla on charging network (I'm skeptical the CCS network will be as good and easy as superchargers, but there is more noise there about doing something), how can Tesla lose market dominance by 2021?
There is a possibility that Tesla will never lose market dominance and will continue to be the one to beat for decades. My prediction is these new rivals will all hit the market like the Chevy Bolt did. A lot of fanfare as the "Tesla killer", initial decent sales, some die hard fans, but after the first year, an "also ran" vs Tesla. In 2017 the Bolt was the #2 selling EV in the US behind the Model S. This year it's #4 behind all 3 Tesla offerings. It's beating the Leaf, but losing out to the Volt.
When the Model Y comes out, it will likely destroy all these other SUVs on price, range, and probably convenience. About all they will have going for them is a fancier interior which will sell some cars, but it won't bury Tesla. These days with aggressive lease deals most Americans who can afford a Camry can also afford a Mercedes or BMW, but Toyota moves a lot more cars in a year. Some car buyers want to be pampered, but most see it as useless fluff.