The quality over Capaldi's time as the Doctor was certainly lower than during Smith's period, according to the AI ratings people give after each episode, but they're higher than Jodie's are. Where Matt's stories averaged an 86/100 AI score, Peter's averaged 82.7/100. Jodie's are sitting on an average of 82/100. All three scores are fantastic, of course. So the quality of the show really isn't that different now compared to with Capaldi. There's nothing to suggest people like Jodie's Doctor more than Capaldi's, or thing her run is better.

More people are watching than were watching S10, that is true, but there are a lot of factors here. S8, Capaldi's first, is actually the highest watched season on average of DW since its revival (as long as you're not counting the special episodes), with 8.3m viewers on average. S11 is currently sitting on 8.86m, so looks to be doing better. However, ratings, as they always do, have been dropping steadily. That's not a criticism, it's just what happens as each series goes on. For S11 to take the 'highest average views' title, it would require episodes 7, 8, 9, and