The short answer is no, but it may be your best option depending on the situation.
For example, in terms of convenience, taxis are great. Especially in bigger cities like Tokyo, you can usually catch one within five minutes (just raise your hand and the driver will see you). Plus, bus schedules may not work in your favor depending on the time of day, and navigating the various platforms, exits and train lines at stations can be a major hassle.
As for affordability, taxis are pretty expensive starting at 730 yen for the first two kilometers and then continuing to increase with distance. Highway tolls will add extra costs and fares can rise during peak hours. But again, if you’re traveling in a group of 3 or 4 people, splitting the cost can make it more or less the same as using public transportation–sometimes even cheaper (especially for short distances).
Overall, my best advice to you is to consider your specific situation, and choose the transportation option that best suits your priorities (affordability, efficiency, convenience, etc).
Learn more about taxis in Japan: https://www.japan.travel/en/plan/getting-around/taxis/