Roku stick doesn't offer 4k streaming, is less responsive, and has less processing power than a Fire TV does. That's why it's a downgrade.
As I said I'm perfectly happy with PS Vue, but I would be curious to check out Youtube TV. It would be pointless to buy a Roku stick to see if I like youtube TV because I would not spend $500 buying Roku Ultra's to move everything to youtube tv. The only way I'm going to check out Youtube TV is if Fire TV's support it, which was my original point. Does that make more sense?
If I were starting from scratch the Roku Ultra definitely seems like the way to go, I wish more of these options were available when I got rid of cable