Excellent post! Sadly, I think their relationship was doomed from the beginning. As you said, they're very different women so that didn't help but the media definitely added fuel to the fire. Last time we had 2 royal sisters-in-law was Diana and Fergie and unlike Meghan and Kate, they were cousins, best friends already and had an incredible bond but I think the media expected Kate and Meghan to be as close as Diana and Fergie were from the very beginning and that was never going to happen or it would've taken more time so instead of letting the relationship develop, they pitted them against each other.
Not all sisters-in-law are friends. I have 3 and we're not friends. We're not enemies. We get along fine when we see each other but they have their lives and I have mine.
It's also interesting how there's so much focus on the relationship between Meghan and Kate when the rift is clearly between the brothers and not the wives