First, I’m not sure it is necessarily viewed as ‘offensive’.
Second, the origin of the masculine gender as reference, is Judaic, and stems from the principle of ‘fatherhood’, in turn, stemming from the cocept/principle of ‘first cause’;
Third, attempting to ‘sexualize’ God, or to project upon God, a gender–essentially a restriction–is essentially a species of ‘anthropomorphism’, as God, the Creator, the First Cause of everything, can not be bound by any sex or gender.
Fourth, when God created Man, He created him in His image–and that extends to woman (Man and Woman, were both, created in His image–there is simply no biblical or Traditional basis to counter this–at least none that I’m aware of, anyway).
Frankly, I am not aware of any express prohibition against referring to God, in the feminine, or even any patent offense to be inferred therefrom, without any other malice to support offensive intent.
That said however, we use the masculine pronoun out of respect, first, and secondly, out of convenience.
Respect first, because to refer to God as ‘Father’, or ‘The Father,’ or ‘Abba’, is to respect and imitate Christ, for this is how Christ addressed God–and how Christ taught us to address Him–hence ‘the Lord’s Prayer’ begins, with a respectful and affectionate approach: “Our Father” (by which we also refer to the prayer). Also, because the ‘Sonship of Christ’, the 2nd person of the Trinity, was revealed to us, in terms of a ‘Father-Son’ relationship. Hence we respect both the First and Second persons of the Trinity, by respecting the terminology and frame of reference, they bequeathed to us.
NB: while emulating this is indeed a sign of respect and reverence, it does not necessarily follow, that to deviate from that, is to show disrespect. But it would certainly appear to be more respectful, and more reverential, to respect that paradigm.
…and out of convenience, for obvious reasons, amongst which are: it is much more consistent with scripture; it has been practiced for centuries, and is deeply engrained in our psyche, and in our Tradition; and it fits the frame work of a family, in that the Church is the bride of Christ–and Christ therefore, the ‘Bridegroom’ (i.e. masculine); Mary, the Queen of Heaven, the Holy Spirit, her spouse (again, masculine); Christ came to establish His ***King***dom (masculine); Christ, the Holy Spirit, and ‘the Father’, are all One, and all referred to in the masculine, and all occupy masculine ‘roles’, in numerous typologies, frameworks, analogies, metaphors, allegories, etc, etc, throughout the Bible, Sacred Tradition, etc…
Hence it would be highly inconvenient, and counter-productive, to go against the grain, when the grain is so layered, in the same direction–ie–referring to God, in the masculine.
CAVEAT: This is not authoritative, and I make no claim or pretense to authority here–just my humble opinion. As always, I welcome correction, to my posts–just some times, such as here, it warrants posting a caveat–lest anyone should mistake my post for something more than it is–one humble believer’s take.