Why is The Fine Tuning Argument an Argument?

Can someone explain to me why is Fine Tuning Argument a relevant argument Argument. As for as I understand the Argument goes that since the constants of the universe require some very precise values otherwise the universe might not exist.
What I don't understand is that how are the values relevant,
Like 1) the reason why 'G' gravitational constant, 'c' speed of light etc. have some random value is because of the way we define what 1 meter is, what 1 second is, etc.
2) We also have no way of knowing if gravity, strong and weak nuclear force, EM force, are different phenomena, it's totally possible they just appear different and in essence the same thing. (So increasing force of gravity might just change rest of the forces automatically such that universe is possible)
3) We also have no way of knowing that if the universe created by just increased gravity would result in an equally viable universe with different laws of physics (Example a universe where Force is not Mass*acceleration)
4) Even if it's that's not the case we can only exist in a universe where all this is possible so even if such universes exist we would have no way of knowing or finding out.