TBH this is a list of "I recieved changes so im being played a ton" and "the meta shifted just enough to make me stand out again" then "Im consistant because my kit allows me to be" The first quote applies to Darius, Garen, Morde, and Skarner clearly. the second is MAINLY referring to Vayne with MAYBE Irelia and fizz in there. The third is mainly dealing with Xin, Irelia, Annie, Fizz, and Kalista.
To the people saying Vayne is way to strong right now and "Well C9 player her and they destroyed TiP cause of her" most of the comps TIP played when C9 had Vayne were tanky as balls so of course she is going to rip through the she is a TANK KILLER her kit is literally designed to kill tanks.
The juggernauts are being watched for now for what adjustments will be needed as we see they hotfixed Darius and Skarner already. Those hotfixes might not have been what they needed or could have been to much in terms of Darius as ive seen him doing really well since his hotfix.
Xin, Irelia, Annie, and Fizz have always been good solid picks in Solo queue because they are easy to play most of the time and are easy to get a lead with because of their kit simplicity.
Kalista is there cause people like to hop around idk what to tell you there plus her rend is stupid strong at securing objectives.