In my city in Romania, public transport is about the same speed as walking. So I'd say Barcelona has great public transport, based on this limited analysis.
Hence, citations neede. What exactly was bad? Did you only try driving?
From El Prat to where, do you think would be a fair analysis?
The idea that public transport has been designed for tourists is preposterous. The network of public transport extend far away from the touristic places.
Most tourist, and most expats in my experience (I'm thinking in those that don't bother to learn any local language), stay in three or four neighborhoods and think that that's the city and get their impressions from those few areas.
That's the reason you always hear the same histories: pickpockets (stealing from tourists), dirty (drunk tourist peeing in the streets), etc
That doesn't sound all that great to me. Here in Tokyo, driving is generally not significantly faster than public transit, though of course it can vary a lot depending on your two endpoints. And of course, if you add in time to find parking, that usually makes driving very unattractive (though this doesn't affect taxis of course, so those can be attractive for some routes if you have tons of money you want to waste because they're not cheap).