How is Tesla leading the pack? It's (still) in a high-end niche with small volumes while others (such as Renault-Nissan:
Combined Nissan LEAF Renault ZOE Sales Exceed 280,000 Worldwide ) are selling in the EV mass-market segments long before the Model3 is ready.
And Tesla won't be alone in its high-end EV niche once the German makers (Porsche, Audi, Mercedes...) offer EVs in the same price categories. Tesla will be attacked from both ends.
Tesla also isn't able to execute and ramp up, otherwise the Model X would be on sale since late 2013 (or at least late 2014). I don't see how Tesla's constant delays coupled with more and more competitors offering longer-range PHEVs and EVs (especially in the segment where the Model3 is supposed to launch) can be good for the company.
EVs as a whole are still a small niche in the passenger car market - and that (even if it's a growing) niche is getting very crowded until 2020. There are also giants like Ford or new entrants like Apple that will sooner or later make a move.
Aah... you're mixing your tenses.
Let's talk about the present tense first:
I said Tesla is leading the pack, not "will lead the pack".
They are leading the pack because they have no competition in their current niche, which is a high-end, long range BEV. This is an undisputed fact and if you have no competition then not by my opinion but by my very clever deductive inference they are leading the pack.
With regards to battery production and battery based products other than cars (but let's agree that in order to build cars you need a lot of batteries) I too believe they are leading the pack. This is because they have the most aggressive plans I know of of scaling up battery production capacity (together with their partner Samsung) in the Gigafactory. Now, we all know of your calculations claiming only 14% of the Gigafactory has been built. My argument is based on the fact that 14% of a factory is more than 0% of a factory, and to get to 100% you usually must pass the 14%-stage (in my experience is very uncommon for production facilities the size of some of the world's largest known structures to suddenly appear out of thin air).
Now let's switch to the future tense:
You say "Tesla won't be alone in its high-end EV niche once the German makers (Porsche, Audi, Mercedes...) offer EVs in the same price categories". I would be careful to say when, but rather "if". And when/if these other OEMs are ready to offer such a vehicle, what makes you think Tesla hasn't moved further forward with regards to features, capabilities, price/value for money? Tesla is a moving target. I choose to base my predictions about the future on the current state of affairs and what Tesla has shown us being capable of v.s. what the other auto makers you mention have shown us being capable of in the last few years. You are obviously basing your predictions on some other weighting of the known facts, which is perfectly fine, but please don't confuse your assumptions with facts.
Last let me adress your statements about how Tesla will suffer massive competition in the "mass-market segment". My belief, again opinion not fact, is that Model 3 will be a high-end mass market car. You seem to think for some reason it will be a general mass market car. I base my analysis on words straight from the horse's mouth: Elon has said time and time again that the Model 3 will be directly plotted against the BMW 3-series. The BMW 3-series is, at best, an upscale or high-end mass market car. Don't confuse medium sized car with cheap car. What are you basing your analysis on?