tiawd –
The Baal Hatanya did not only “not make up the idea of the neshama being a חלק א-לוק ממעל out of nowhere” rather it is a well established fundamental idea before and after the Baal Hatanya with sources before and after Lubavitch.
The Nefesh Hachaim also uses the word גמור in his statement “מבחי’ הנשמה דלהון ולמעלה הוא אלקות גמור”, the meaning of כביכול is also not as simple as you suggested.
One thing is absolutely clear and unanimously stated by all the sources here; as much as it is a creation, the Neshama is a unique creation sourced much higher than all other creations, this is the point of the Baal Hatanya and the Nefesh Hachaim here.
As the Chovos Halevavos writes, only a fool spends his time trying to understand the essence of HKBH, when you finish (כביכול) explaining the essence of HKBH you can expect to understand exactly how mamash or not mamash, gamur or not gamur the Chelek Eloka Mimaal is.
The main “equivalence” intended in my last question was that as stated here above, in the context of a proper understanding of אין עוד מלבדו and the true meaning of Hashem’s Oneness your “questions” are just as much of a “Klotz” question as that question is, certainly not grounds to call into question the legitimacy of the Baal Hatanya or those inspired by him and suggest that there is any problem with their אמונה.
As stated above, when it comes to the actions and behavior of people which is what really matters at the end of the day, the damage of people who underestimate the power of this idea is far greater than those who you think may have gone “overboard” with this idea.