I'm a silver adc main and throughout the last week I have gotten to see my fair share of the two new League of Legends champions, Xayah and Rakan, and in my opinion they are extremely overpowered when together and very solid on their own. Xayah and Rakan's design I think is fundamentally solid. They are partners in crime and lovers and thus should work very well together, right? However, this brings up a problem. You don't want the champions to be too strong when together or they will dominate and have to be banned and you also want them to be strong enough on their own without needing the other, which is a big problem because it's really hard to balance for both. If the champions are good on their own and only get stronger when they are together then it becomes a priority to keep them apart at all costs and that is the case now.
If someone on the enemy team picks one of them you need to grab the other or concede to a losing bot lane. The extra range, damage, and utility that having both together provides make their laning phase extremely strong. This mostly affects Xayah. I believe that Rakan is extremely good. He provides great amounts of utility and mobliity and functions perfectly fine on his own. Xayah however can have a rough time early without a support like Rakan that can get her out of bad situations with ease. Xayah is extremely strong when ahead and almost worthless when behind. I've only been able to play a few games on them because they are picked and banned almost every game so its been difficult but that is what I've seen.
Their duo lane is extremely oppressive and extremely hard to deal with unless you are playing high mobility adcs who can escape from Rakan's engages and Xayah's E damage. I think Xayah is in a good spot balance wise. If she is punished early it is hard for her to come back, but Rakan is whole different beast. He will always be good and relevant with his kit. Rakan has a ranged melee auto (like Thresh), harass, sustain, shields, different movement spells, an AOE knockup and an AOE charm. His kit is ridiculously overloaded. This is countered by the fact that he has pretty low health pools and damage, so hard CC on his engages can shut him down, but he just has a ridiculous amount of outplay potential in his kit that makes him hard to deal with. When pairing him with Xayah it makes it almost certain that she will get ahead in lane and become the monster that she can become with a couple kills.
So in my opinion, I think Xayah is fine the way she is, but Rakan might need some fine-tuning on his abilities to make playing against him on the rift a little more fair. He is easily the strongest of the two and is extremely viable on his own, a bit too much in my opinion.