The thing is, is there is no such thing as "Third tier devil fruits". In the right hands, any Devil Fruit can be a Top Tier fruit. Luffy proved that with the Gomu Gomu no Mi. Even with mid level Haki at the time, and no awakening, Luffy, with G4 was able to overpower Doflamingo and Katakuri, whom both had awakening.
And you and I both know that Luffy's fruit, isn't any more of a "God Fruit" than Sengoku, Kaido, Katarina Devon, Marcos... etc... All of their fruits are based on God like beings, and two of those people aren't in the realm of Top Tiers. Luffy is there, even if you removed G5 from the equation.
So just because someone has a "God Fruit" it still doesn't make them Top Tier, unless they are able to utilize that fruit in a manner that gets the maximum out of the fruit.
If you gave the Nika fruit to any other character but Luffy, even in it's already awakened state, it still would be considered a "Third Tier Fruit" because the likes of Law, Kidd, Blackbeard, Akainu, Whitebeard, Kaido, Big Mom, etc... etc... would never be able to utilize it like Luffy can.