Its really not true. You have to be lvl 20 summoner or higher for the mini-fork battles but the fame isnt lvl 3. I had and still have level 0 fame in norg and got leviathan and ive dragged other people to norg who have done no norg quests and get the building trust dialog from the norg fame checker who have also been able to get leviathan mini-fork. So norg mini-fork = 0 fame, lvl 20 or higher summoner set as main job, have to talk to the other one (not the taru) of the 2 orastery people on the dock in norg.
I'm from windy, so i had lvl 2 fame when i got ifrits mini-fork, and ramuh's which was in mhaura and shares windy fame. bastok and sandoria I had 0 fame in when I got shiva and titan. Garuda is rabao fame which is sandy fame and I had 0 fame in sandy when I got her. Anyway youre going to need fame at some point and it's really not a bad idea to start building up your fame whenever you can, but as far as the mini-fork battles go I really think its probably lvl 0 fame for all the mini-fork battles.
Prime battles (lvl 60+): have summoner unlocked, you can get the whispers with any job class. Take your 70+ rdm etc, get the whisper for your lvl 1 summoner job. This was the classic pre-minifork way of doing it and is the reason why you can sometimes see lvl 1 summoners with fenrir
/cry. I want fenrir.