There have been excellent posts on TMC laying out the many components of Tesla's 'moat' i.e. why they cannot be caught or passed by competitors with more resources but late to the party. It is the sum of the parts that determines how large the moat is and how long it will keep Tesla the worlds most advanced and effective EV manufacturer. Unlike a Wall, the individual components of Tesla's mote are not static but changing dynamically over time. Some gain while others diminish as what portion of the total moat they represent and the size and consequence of the total moat will increase or decrease as they do. Tesla has built its moat due to foresight, pace of innovation, willingness to take risks if payoff seems large. Even a cyborg dragon will not overcome a large moat unless it exceeds the leaders pace of innovation long enough to catch up and then overtake the leader.
It is certainly true that the single biggest component of Tesla's total moat is deciding to invest in the biggest and best battery manufacturing factory in the world with all that involves in advanced automation and innovations improving efficiency. It is not the total moat.
Elon, J.B., Jeff Dahl, etc. would not agree that cell performance doesn't matter. It's why they support Dahl's group. It's why they watch new developments like a hawk so they will not lose this qualitative portion of the moat. Improvements in cell performance are why a LR Model 3 has 320+ mile range, with good performance, and very low pack degradation over time and cycles. It's why Tesla can develop and deliver electric Semi trucks with up to 500 miles of range with fast recharge and long lifetimes when others cannot.
Last, JB, Dahl, etc. would not support your assertion that improvements in high performance cells can be as easily duplicated just by slicing up a few samples for analysis. If this was the case Samsung, LG and BYD etc. would be closer to parity with Tesla batteries than they are. I've spoken with cathode nanotech company staff and one point they emphasized is that cell chemistry changes effect every aspect of the cell performance characteristics and those matter to the end users of batteries.