Yes, this is already the case in China and I suspect in many places around the world. In Shenzhen, taxis are very cheap and available within 100m around the clock pretty much everywhere. Even if you drive on average 1 hour per day which is very unusual in a high density city, owning a car would probably be more expensive then always taking the taxi. Yet, a lot of people still purchase cars (mostly luxury brands).

I suspect this is the case almost everywhere in the world. A car's purchase price + gas + maintenance + taxes easily surpasses what you'd spend on taxis, even in a 5 year period. The keys to car ownership are convenience and the emotional aspects.

Taxis don't go everywhere.