Islamic texts say "be different"; not "be mostly different". They never gave it a 'holistic context'.
When the Prophet (ﷺ) spoke of imitation v. being different, he spoke on the individual action level.. i.e., do not imitate them in an individual action unique to them, period! He would say non-Muslims do A so ordered we do B; non-Muslims do C so Muslims do D instead. (Plenty of example, from shaving to dying hair, the list goes on).
So the expection is not to imitate them in these actions, even if you are 'overtly Islamic' in all other ways. Remember, the audience to whom he was speaking were the Sahabah who were righteous and overtly Islamic yet the Prophet ordered them with these commands and they abided by those commands; so too do we have to. This also shows that even the overtly Islamic cannot imitate any particular non-Muslim actions.
Beyond the texts not supporting a holistic approach, think about the fact that a holistic approach opens a can of worms regarding how much is "too much"? At what point does any imitation become too much imitation? Etc.. - Reality is, any imitation inevitably leads to greater levels of imitation, to the point that it becomes "span by span", as the Prophet put it.
The Prophet (ﷺ) said, "You will follow the ways of those nations who were before you, span by span and cubit by cubit (i.e., inch by inch) so much so that even if they entered a hole of a mastigure, you would follow them." We said, "O Allah's Messenger (ﷺ)! (Do you mean) the Jews and the Christians?" He said, "Whom else?" - Bukhari (7320).
Based on all of this and more, Islamic scholars will say you are "imitating disbelievers" based on a single action of theirs that you imitate (e.g., celebrating their festival). Rightfully so.
Hope this helps shed some light.