Honestly, just tweaking a few actions wouldn't cut it. The whole sea of fish has to be adjusted or some fish needs to be cut/deleted or tuned down.
atm (Patch 5.55) there are more than one THOUSAND different kind of fish to catch - even if you don't count in spearfishing.
I want to give two... no, three examples of what's most wrong with fish(ing)
1. Too many useless "common" fishes:
The most annoying kind of fish. There are usually 1-2 of those in every area. e.g. Rak'tika Greatwood: Yellow Pipira and Clawbow. Both serve no purpose other than filling ALL Greatwood fishing spots as most common fishes. No useful desyn, no mooch options, nothing of value (such as leve or job quest). Even worse: when you mooch for bigger fish, they are also a common result, just adding to their annonyance level.
The best example is Lake Tusi Mek'ta: For the Priest (big fish) you need: Clown Tetra -> Eryops -> Priest of Yx'Lokwa
Yellow Pipira and Clawbow are common and often take your bait during Clown Tetra's cast time window (they are only ~3s apart), but even if you happen to get a Clown Tetra, and mooch it, Yellow Pipira might take the bait AGAIN. There is neither a bait that's only (or mostly) biten by Clown Tetra nor an action that prevents Yellow Pipira from taking the mooched fish. But that's not all, I will take on this spot later.
2. Big fish that require long or hard (difficult/rng) preparation:
Take Warden of the Seven Hues (Prism Lake/Yanxia) for example: You need 3 prismfishes from mooch options, each during 0-4 ET and 4-8 ET, and your chances for getting the right ones are ~12-17% (getting the right one is 33% or 25% if green Prismfish is also active - maybe less -> 50% once mooched), and you need 6 in total (2x3), additionally, you need 5 green ones during 0-16 ET and the right weather. So, you have ~11min to get 3 Indigo and 3 Firelight fish each, and at least ~22min for 5 Green. Thus, your prep time is roughtly - and most likely - 30min... well, that means IF you didn't fail to get 3 of the first 2 fishes in time (I have failed probably 3 windows because e.g. I didn't get 3 Indigo 'cause of no violets, or White Goldfishes take the bite after mooch first.)
Once you fulfill all requirements, you get the 2min 55s Intuition buff, and now you have a CHANCE to catch the Warden (no idea what the real chances are). So, you spend all of your GP on Chum, maybe one Surface Slap... oh, no bite? Too bad. Oh, you had a bite? Too bad, it got away. What, you were lucky and had more than bite? Too bad, all got AWAY.
THIS should not be a thing. You need more than 30min, just to get a (few) chance(s)? The catch rate should be (at least close to) 100% once you have min. gathering.
3. Big fish as requirement for... big fish:
Yes, I am looking at you Ruby Dragon. Apparently someone in SqEx thought for Stormblood it was a brilliant idea to set big fish as requirement for another big fish, either as Intuition buff (catch one or two + other fish) or as mooch bait.
So, let me get this straight... someone over there... actually thought... "Hey, you know those big fish with probably less than 10% bite rate, and less than 50% chance to NOT get away, yeah? How about we put another big fish on top of these big fish with the same rates?! Our fisher players are going to love it! This might be the best idea maybe ever!"...? /irony off
Unfortunately, this didn't stop with Stormblood (or just Ruby Dragon). Now, let's go back to the fishing spot of Lake Tusi Mek'ta: In 5.55 they introduced the Greater Serpent as a new big fish... with Priest as its bait... wow, HALLELUJA! It's already bad enough with just getting the Priest hooked, but now you have to mooch it for the Serpent? In less than 6min? Holy moly, pray to our bois YoshiP and RNjesus, and take on your seat belt, this gonna be a looong ride! (other examples are Lancetfish in the Tempest (needs 2 Mora Tecta), Aquamaton in Kholusia (1 Shadeshifter + 5 Shapeshifter) and Listracanthus (req. Jaws of Undeath as mooched bait).
Now add any other elements into this: short time window, long cast time, rare time window (some take weeks to be active), low hook rate, low catch rate, or any combination of those. Many of those big fish require weeks or even months to catch (only one of ~12 guys got Cinder surprise in the last window I took part of, and they told us, they were on this one since the patch - almost 3 months!) This takes longer than your average Ultimate prog!