They are the strongest element of this era for me. Whatever issues are cropping up for me with this era I think the Fifteenth Doctor and Ruby are a solid team.
I don’t feel Ncuti has had much chance to properly show us what he’s capable of as the Doctor but when he does I think he’s great.
Millie Gibson is almost supernaturally talented I think. The structure of, length of and approach to the season wasn’t ideal for me but she emerged as its secret weapon. Like Ncuti though, the limited nature of the season (length and approach) didn’t fully do her justice but she had a 73 Yards unlike Ncuti who I don’t think has had a barnstorming showcase for his Doctor yet. Boom came closest (another episode where they were both absolutely fantastic) so I feel like I have more of a handle on Ruby than this Doctor.
I wish she was full time still but the introduction of a new companion may help Ncuti emerge even more as the Doctor, which I’m really excited to see.
But short answer - they’re a great duo. Ruby particularly.