In stating that the roles played by Albert and Armand are homonormative, or are "trying to perform as a heterosexual relationship," one is defining the heterosexual relationship as natural and normal while casting the queer relationship out as strange and wrong. When one is trying to act out a certain expectation, it is assumed that what they are trying to display is the more correct version of themselves. This works toward eliminating the conversation around the naturalness of a queer relationship. This ideology can be internalized without the individual affected ever even questioning the role of a queer relationship within a society. This begins to trap the individual in a cycle of trying to perform different "acceptable roles" without ever examining whether or not anything is "wrong" about their own true role (that role which occurs naturally within them).
While it is clear that one familiar with the politics of heterosexual coupling would see it as obvious to label Armand as "the man" and Albert as "the woman" in the relationship, if one ignores the fact that society tends to perceive heterosexuality as the correct manner of being then these labels do not make sense and can be portrayed as comical (Why would one try to mimic something that is so strange?). Following a similar vein, it would be possible to reverse the timeline portrayed by critics of the action. How can we simply assume that gay relationships are mimicking heterosexual relationships? Perhaps homosexuality evolved a certain power structure within a sexual relationship, and heterosexual couples, wanting to be more similar to their gay counterparts, mimicked that power structure of the penetrator and the penetrated (the woman becoming the obvious choice to represent the penetrated due to her inability to penetrate with a natural sexual organ) and formed today's gender roles around these roles. In any case, it is easy to see that defining Albert and Armand's roles simply as performing homonormativity and ignoring all other possibilities leads to limited discussion and could potentially lead us to miss important points of discussion.
The point you made about trapping the individual in a cycle trying to perform acceptable roles. I didnt think about it in that way and I feel that it is a good point to understand when thinking about queer cinema. I also agree with your last point that ignoring all other possibilities leads to limited discussion. How can we have a discussion without realizing what is defined as homonormative and heteronormative. So good points!