Ok, even so, i managed to get 40 blimp fish in a day with the overlap, wasn’t bad at all 
Flounder, Perch and Kyalakin all definitely have spots with no overlap, unsure about jelmiry.
Not every spot for blimp has probably been found yet so theres still chances you can find location where it does not overlap, blimp is more tricky though as it uses ingredients common fish do too (minnow), as it’s your introductory Legendary fish (and seems to bite more than other legendaries aswell; for me atleast)
And you can make potions without the legendary fish, it’s just more efficient to have them, thus allowing players to still make their pots even if they can’t find (e.g. newer players or players not really into fishing)
Also i do believe it’s not the intention that everyone knows how to catch every fish or be able to do so on a whim: Fishing Myths @riley - #14 by Riley_D
Beyond that, like you said, it’s week 2, we still don’t thoroughly know the legendary fish location times and conditions plenty more data needs to be gathered, saying they specifically are too difficult now seems a little rushed?
I am in total agreement with the lesser fish such as sunfish & catfish etc.