I get why they didn't sign Cueto or Kluber. First, I'm not sure how big of an improvement they actually were.
Second, Kikuchi and White are complicated. White is out of options and I know people often assume that Kikuchi is willing to go to AAA bc he offered to go last year but I wouldn't count on hm being willing to start Opening Day in Buffalo this year. It's one thing to escape the pressure when you can't get the ball over the plate in July, it's another thing to forego the fresh start of a new season.
The team has little depth as it is so losing Kikuchi or White doesn't make sense. Could the team really enter the year with both in the bullpen? Perhaps, but I think it would have negative implications for their SP depth anyway as I'm not sure both guys would be kept stretched out enough if they are both in the pen.
So yeah, I get why they did what they did. But it still doesn't mean I love the rotation depth. I doubt the team is that thrilled with it either but is willing to ride it out for now.