So... if we take that at face value, why put so much emphasis on the fact that it will definitely not happen to Momo ? She is also royalty, she is no more in love with Aki than the queen and Juju were. Their situations are pretty much identical. If the author (and defenders) state that being forced to marry a guy from another country is okay, and the characters will find happiness anyway, then shouldn't you also be content if the same happens to Momo ?
Because the fact this happened to the Queen, means she'll help Aki and Momo so it doesn't happen to them, she can sympathize because it happened to her, so this time it's different to her own case and won't happen to the main duo because they have support from someone that understands their situation. And the only way to achieve this was to have the previous generation be affected by it.
I mentioned my profile picture before, but seriously read Urara Meirochou, there is no better manga to portray the breaking of fate away from a tragic ending that the previous generation suffered, better than this one.