So Let's Talk About Borders and Ribbons
My main criticism about these is the non-visibility by opponents. We'll start with the ribbons.
Honestly, I'm not sure why you, Riot, decided to make these only visible to teammates EXCEPT the honorable opponent one. I honestly don't think of my team composition (or the opponent's) differently by seeing any ribbon at all, let alone what color the ribbon is. I just came from reading a thread about ribbons and the incentive for giving them and I feel like the inability to see opponents' ribbons gives players a skewed sense of how many ribbons are actually around out there. It would seem to me that seeing more ribbons on a consistent basis would drive you to act in such a way that you promote the ideal of those ribbons (without abusing the system, of course).
My sentiment of ribbons is somewhat echoed for opponent's rank borders. I understand that you want to eliminate a feeling of defeat and negative attitude simply by seeing the border but I don't think this was a widespread issue. If anything, seeing that I would most likely be laning against a gold Caitlyn would make me try to step my game up and play better for my team. This is the same reaction I had when I saw people with alternate skins when I first started playing and the same feeling I had when I played my first ever ranked match. Your desired effect is also lessened by the widespread use of lolnexus and lolking to view the team comps during the loading screen. The only difference is that the negativity would start once the game has actually begun rather than before. Furthermore (last point), I don't see the difference between somebody getting disheartened/negative based on rank borders (or ribbons) and having that same reaction to something such as team composition. I see this all the time in ARAM and still some in normal 5v5 especially if one little thing happens in the opponent's favor.
Thanks for reading. Hope its coherent enough to understand my points.