Culpability is almost completely irrelevent to 915, its determinations are based on perceptions of the gravity of objective sin, public scandal and the dispositions of the Communicant. You have seriously misunderstood this Canon from what I can see.
I am not the one bringing culpability into the judgement of Canon 915. Rather, it is those that argue that culpability in the sin of remarriage can be mitigated to the point of rendering the new marriage not a “grave sin”, and therefore not subject to Canon 915. If culpability is not a factor then I see no way in which Communion can be given to those in irregular marriage given Canon 915, and the fact is that AL and all of the published guidelines discuss subjective culpability as the reason for allowing Communion.
The argument seems to go like this: the remarriage is not a grave sin due to factors that mitigate culpability, and since there is no grave sin Communion can be administered. What is not clear is how this can get around “manifest grave sin”, because the appearance of grave sin remains as the matter of culpability remains internal and hidden.
It is only by accounting for subjective culpability that the previous prohibitions on Communion for those in irregular marriages are modified, and this can be seen by the justifications presented in AL and the published guidelines. If we are to bring subjective culpability into the question of “manifest grave sin”, so be it, but let’s not pretend that there is no apparent break with previous practice. At the very least a clear teaching of what is now meant by “manifest grave sin” is needed, since it can no longer mean that a grave prohibition has been objectively and publicly violated.
I can understand that there are real life circumstances that aren’t easily shoehorned into Canons, and that sorting out culpability is both personal and messy. I even support the Argentine Bishop’s guidelines, including the provision of allowing Communion to those in certain irregular situations. My main concern is the underlying moral justifications for such allowances, and with the manner in which these exceptions are implemented. Unclear or erroneous justifications lead to further confusion and error.
Furthermore, I stand by my interpretation of the Maltese guidelines. If it is as you say, that Canon 915 remains in force as is, then there can be no room for “feeling at peace with God” allowing access to the Sacraments. The “manifest grave sin” remains, as the grave matter remains, and the formal sin and disposition have always been hidden and not manifest. If “manifest grave sin” refers to formal and not material sin, then it has always been a contradiction in terms, but the tradition appears to have been that it is the grave matter and not the subjective culpability that is understood in this Canon, and the grave matter has not changed as evidenced by the line of reasoning in AL and the guidelines.
Peace and God bless!