I think that as the universes have matured, spice is not as difficult to get as it used to be a decade ago. And that was one of the main reasons for using battleships. They cost no spice to build.

In time, people also began to see that batts were far more expensive to fly, so saving spice in building them didn't help if you were intending to actually use them for regular attacks...

Then of course, the only argument left for batts is the tougher shield. Adding more phoenix to a phoenix attack will solve their weaker shield, or adding some bullet catchers will help too. Basically, batts is still a great ship, but only if your opponent is a turtle and cannot run away from you...

There is another big advantage of the Phonix, it is faster then a BS. Thisfact reduces the danger of beeing intercepted, especially from BS.

low fuel consumption, speed, attack and Improve warp engine is more expensive than diffusion engine.