Its worth noting that you can have other legendary creatures in your main deck too if you want, as long as theyre in the right colours
An extra turn, a battlefield sweeper, and a reanimation spell stapled to a removal spell are all solid effects in the format, but the condition of having a legendary creature or planeswalker in play to cast them makes them just awkward enough that many people choose not to play them
In Creative Energy, Cayth is likely just going to be a good source of value and bodies, but that doesnt mean they dont have potential
Certain cards in the deck can help to discount spells, but this is only a band-aid to the bigger problem
Take out the random stuff
This is reportedly to cover the additional cost of licensing each UB set