I must be weird. I travel over 100 days a year. I do a lot of walking, sometimes rent cars, take public transportation, etc. I take taxis etc. relatively rarely.
Each of those options is perfectly fine for transportation if you planned and or intended to use them, what I mean is that whenever I've used a taxi or taxi-like service, car rental and/or public transportation would not have been a valid substitute or even possible.
Car rental because you have to pick up the car and later drop it off and the costs are significantly higher than a taxi, and public transportation because it's slower, more crowded (therefore more difficult with luggage) and doesn't always go directly where you want to go.
On a city-wide scale you can't expect car rentals and public transportation to be a valid replacement for a taxi/taxi-like service.
I have lived in Europe, although not Poland, but my point is not that public transportation is not useful, just that it's not always a suitable replacement for a taxi.