Don’t know if any of you watch Dave‘s World of Fun Stuff (he’s a luthier) on YouTube but he says he always uses Rotosound Swing Bass because they hold their tone and last the longest.
Let me say right now that no set of roundwounds will ever outlast a set of flats. Jamerson kept his LaBellas on until they broke with wear and rust, and they never threw him out of Motown...
No, if you like the tone of flats, then, no matter how much the outlay (eg Thomastik-Infeld TI344 Jazz Flats, bloody amazing if you like light and flexible, but havin'-a-giraffe prices*), they work out cheaper in the long run. The expensive bit with flats is trying all the different sets! Once you've settled, they're cheaper. Bit like M+ tyres...
*Made in Vienna, doncherknow...