I'm having troubles finding Thunder King Rai-Oh good this format. Sure, they can never be bad cards, and will serve some purpose in a duel, but most of the time, they act only as beat sticks.
The main problem Rai-Oh has this format would be Card-Car D and Inzektors. Rai-Oh is all about sitting on the field for as long as possible and stopping your opponent from going off.
Card-Car D's effect cannot be stop by TKR because it draws. This made all the difference because CCD is played in almost every deck in 3's now. The 3 CCD helps the player draw into field resetting cards like Dark Hole and Torrential Tribute. When your opponent has a card set face down, it is best for you to just swing with the 1900 TKR instead of getting another monster out. Over-committing to the board is extremely bad this format, and its one of the key points that separates a good player and a bad one this format.
I'm borrowing some terms here. If your opponent has TKR on the board, you can safely sit on a board cleaner and your opponent essentially gives you 5 turns. With CCD, your resources doubles the ones you could draw without it, and you can easily make a come back by trading one for ones and maybe sometimes even negative ones, just cause you have so much advantage.
Since we don't really search for cards this format, and have tons of monster removal teched in. eg Lair Wire. TKR just can't stay on the field for long enough I felt.
The other reason why TKR isn't good, is because Inzektors are the top deck.
TKR means nothing to Inzektors because they can unequip Hornet, pop it; equip Mantis, run over it and even plays like equip some random Inzektors to Centipede and run over TKR.
TKR is an antimeta card, and the worth of an antimeta card is almost always determined by how good it can take on the top deck of the meta. In this case, it gets completely destroyed. Sure, you might pull out the argument of the Inzektor player not having the right cards in hand and can't search them out with Duality. But, in that case, any beat stick will do, not only TKR.
I guess these are 2 of the many reason why HERO beat drop TKR from the main completely. At least for me, I feel that TKR needs to rest for a format or 2 now, since its been doing overtime at both TCG and OCG sides for the past 4 formats.
I guess TKR would not be seeing much play in the main deck (OCG wise) till Inzektors get hit, since they are the main reason players stray away from cards that can't be chain. Just some thoughts.