The link you provided refers only to the LG supply deal exclusively for Model 3 / China.
Tesla owns the largest battery production facility on the planet (Gigafactory 1 in Sparks NV) which supplies battery in partnership with Panasonic.
But the difference is Ionity is CCS and all EVs can charge at its chargers. CCS cars can use any CCS provider like Ionity, FastNed, Allego, etc. which is the correct approach. I can fuel my ICE car at any fuel station and I should be able to charge my EV at any charging station.
You're making the case for CCS. I agree with you. A common charging standard is better for everyone, just like common internet protocols allow Facebook and Apple to be successful.