@Doombybbr I offer to play you in the Valerie vs. Rook matchup. Are you a strong Rook player? Or are your observations based primarily on plying against Rook? I would offer to play DeGrey too, but my DeGrey is weak; perhaps someone else would be willing to fight you.
I don't feel it's very useful to theorycraft these things on the forums, or to make sweeping claims about balance on Day 1; better to actually make a claim (Rook is overpowered) then challenge strong players to prove this claim. Keep in mind we've been fighting "this Rook" for about a year now internally, and have nerfed him twice in the past because he USED to be as oppressive as you are saying, but he's been weakened overall a great deal and some of us would consider him possibly low tier in the scope of the characters that exist.
On restricting design space; as the dev team is mostly fighting game players, we're aware of how strong his mixups are. They're intentionally powerful, and his approach game is strong to supplement it. His close mixups aren't too powerful in our opinion, even barring reversals, because they key off of a normal Throw (Yomi counterable) a lot of the time. His post command grab oki is his worst by intention, because we agree getting all of his mixups off of that would be bonkers. It's actually surprising you'd think a new character we'd create would ignore Rook entirely and come out without any way of dealing with him. This is a fighting game with very few moves; its been very easy to turn the knobs and make tweaks so far.
That said, part of the reason he has been nerfed a few times already was because at the "convention level" (meaning demoing for complete strangers at PAX or Playstation Experience) Rook was completely terrorizing the new player experience. We've made adjustments since then, but he remains the easiest and most powerful character at low levels of play. Some character has to be, so in our game, it happens to be Rook.
The trick is if he's also that dominant at top level, which we've found he isn't. Again, this is where it's on you to actually seek out these players and test your theories. If you can demonstrate a balance issue, we are willing to listen. But it's not useful to state this without fighting my Valerie for example :