You mean at Everton, which is the basis for your opinion.
Much like Ricarlison was great the first half of the year, but when asked to defend and work like crazy when you've been playing football consistently for over a year, I think there's a pretty good reason for him to have slowed down a bit.
Doucoure has not much to do with Siggy, but my opinion on him is what I've seen in the PL, which is the same league Everton plays in last time I checked. He's fantastic. Pace, power, skill, touch, great in the tackle, covers a ton of ground, good passing range, amazing transition player, good in the air, strong on the ball, good decision maker, excellent shot, opportunistic, he's got everything IMO.