Law isn't even favoured generally, he is usually nerfed because his fruit was made too strong initially. He only looks favoured when he's next to Kidd.
Oda doomed Kidd when he made both him and Law df merchants but gave Law a god tier logic defying fruit, and gave Kidd a glorified lego builder. It is impossible for Law and Kidd to be on the same lvl, and this was made evident 3 times now, on the roof, in the fight against Big Mom, and then in their fights against their respective Yonkou opponents.
If there's one thing Oda did here, was stay true to their abilities. Despite Kidd being portrayed as a top Supernova, he just couldn't justify Kidd performing Law lvl feats, he gave Law a far more broken fruit and he constantly hammers down the point that Law is a lot more difficult to deal with than Kidd. I think he picks on Kidd, because his fruit could have been so much more, and if not, then atleast have Kidd tap into haki.