Is it possible to max every art and skill without multiplayer?

Solution 1:

The answer is yes.

Upon beating the game, you unlock support missions (accessible via the back terminal in the BLADE barracks, where you normally do multiplayer interactions).

In here, there are 6 missions (the first 6), giving this amount of BP:

• The Docile Ovis (4)
• The Grand Plot (8)
• Reckless Prone (12)
• Greedy Prone (24)
• Noctilum Nights (48)
• As If a Cloud (60)

The best way to get BP is to repeatedly do the last one - in a good skell, you simply one-shot everything (especially if using an Intergalatic Phoenix or G-Buster), making it the most effective method to get BP post-game.