Why shouldn't I start with Jinpu as my first buff?
By opening with Jinpu first you gain 130p via GCDs, however, by doing Jinpu instead of Shifu first you have a 45% chance to lose a GCD in the long run, which would already result in a DPS loss if you lose a Hakaze.
Tested with the 2.14 GCD tier:
2.46 - 2.14 = 0.32
0.32 x 3 = 0.96
0.96 / 2.14 = 0.45
Addendum: This calculation doesn't factor in auto attacks which would be further in favor of Shifu first via a similar calculation.
Jinpu first also delays your opener burst by a second, endangering your burst hitting raid buffs.
➜ Jinpu first is only a reasonable option in very specific scenarios, for example a re-opener with 3 Sen & 100 Kenki where you measure up one or two lost GCDs (2.88s or 1.92s lost depending on which 3 Sen & 100 Kenki opener you do) and one or two lost auto attacks versus 442 gained potency via GCDs, 106 gained potency via oGCDs, ~50 gained potency via auto attacks and being 2 Higanbana ticks ahead. Even in an extreme case like this one it is in favor of Shifu first if the lost GCD turns out to be a Midare. If you end up losing 2 GCDs then Shifu first is likely to have been the correct choice regardless.