Totally, but the principle applies. If the thing you buy something with gains value faster than the thing you bought then you are effectively losing money.

I would not make a big purchase with bitcoin today. In your example about buying bitcoin in 2018 and then buying a car in 2023, that 0.81 bitcoin used in 2023 to buy a car would be worth ~200k in 2028. Obviously one is far better off holding bitcoin than holding dollars, but it would poor financial decision to buy a car with bitcoin right now.

As a very real example, I bought SOL at $20. I sold 25 of them at like $35 to buy concert tickets. Of course I still made money with my SOL and so I effectively paid $500 for $800 tickets, but the opportunity cost of buying those tickets was a couple thousand dollars.

That is the math. Your argument is the $500 for $800 tickets. That is undoubtedly a great deal. My argument is the if i had the 25 SOL they would be worth $2500 now. Not such a great deal.