If it were PB + Wis mod, it would be better for low level characters, and it would work for EVERY fight, as it wouldn't rely on Long or Short rests.
- L1-4: PB (+2) + Wis mod (+3) = 5 Di points per fight, but can recharge to earn more throughout the fight.
- L5-8: PB (+3) + Wis mod (+4) = 7 Di points per fight + recharge
- L9-12: PB (+4) + Wis mod (+5) = 9 Di points per fight + recharge
- L13-16: PB (+5) + Wis mod (+5) = 10 Di points per fight + recharge
- L17-20: PB (+6) + Wis mod (+5) = 11 Di points per fight + recharge
Many fights you wouldn't even use all your Di points. But you'd be encouraged to, rather than be afraid of running out for future fights.
In fact, you are encouraged to go hard and fast to use more Di points per fight due to recharge. Sounds like you get more per fight, and more per day overall, but it is not unlimited for longer fights.