Who the hell is gtx? I went back through the thread and saw no one by that name.
Sure you can calculate c-rate with percent... if the battery charges to 100% in 1 hour, that's a c-rate of 1C, 100% in 30 minutes is 2C, 50% in 15 minutes is also 2C.
You're wrong about c-rate not telling you anything. At the very least, c-rate tells you how well the cells perform in comparison to other cells. You may not be able to say with 100% certainty that a car with lower c-rate charging adds less miles per time than another car with higher c-rate without knowing any other details, but generally, it's a pretty good indicator of what charging performance is going to be like.
And if all we knew was c-rate, maybe I wouldn't have claimed that the charging performance wasn't good. But that's not all we know. We also know how many rated miles are added in 15 minutes, and sure enough, it's worse than every other Tesla apart from the Model Y with the same 4680 battery cells.
Maybe you think it's good, but I would never want to road trip any EV that takes 2 hours to DC fast charge. Physics dictates that this vehicle is going to use a proportionally large amount of energy to move, so even if it adds 100 kWh in 15 minutes, it's still not going to go very far on that 100 kWh unless it defies the laws of physics and is magically an order of magnitude more efficient than other EVs. A Tesla semi has a rumored 900 kWh battery, but can only go up to 500 miles, so if it charged at a 0.5C rate, that means it would add 62 miles of range in 15 minutes, which is still bad, even though it added a whopping 112 kWh. Tell me that a vehicle added 112 kWh in 15 minutes and I couldn't tell you if it's the best charging EV ever or the worst, but tell me that it charges at 0.5C and I can make a very solid guess that it's not going to perform very well in terms of miles added per time.
