Right now, for fishing, we're at a point where GP management is far less of an issue than it ever has been. Thaliak's favor and angler's arts has really raised the floor up a bit on some of the more trickier GP management fish (like Stethacanthus, Ruby Dragon, Ocean Fishing Routes, Ambling Caltrop), and made big fishing a bit more bearable for folks while opening up new methods of fishing. Outside of material farming, and at the current moment with big fish, GP is becoming less and less an issue, varying with how much you prep AA stacks ahead of time.

A better cordial COULD:
Help improve scores on Ocean Fishing.
Eliminate any chum down-town on longer window straight catch big fish.
Improve yields of material farming slightly.
Raise the floor on Purple Scrip farming.

Does fishing need a new cordial? I don't think so. We have enough tech with Hi-Cordials and Watered Cordials that we're ok at most skill levels.
If anything, I think they should increase the cost of some of the skills (including AA skills) to put back some pressure on GP Management.