Question + rant about dk

I played dk all my life. Got quite far in pvp and pve and I took a break for 6 years. I came back got again similar ratings on dk as before.

But honestly they just keep making frost into god knows what and unholy is so half baked.

Can anyone explain if Assasination or Destruction any good? I wanna try either rogue or warlock to main now. Is it even worth it or should I stay dk after all these years? Now I play more casually so I am thinking is it worth learning new class with my game knowledge from since cataclysm, or should I stick to good ol reliable? Answers like “see for yourself” are great but I am asking advice because not sure.