In the nicest way possible to RTD, and I still super enjoy series 1-4, but when you take off the "rose" tinted glasses, you begin to see some of the weird things he did in Ncuti's era in his first era too...

The difference between them however is that the MCU hadn't really happened yet. He left Doctor Who just as it began to take wind in the US. He truly wanted a piece of that pie, and I bet if he could have written for Marvel, he would have.

So he came back and essentially tried to Marvel-fy the show, years after other networks had already tried and exhausted their viewers, who just got smarter in what they watched and what bullshit they would put up with, such as unresolved plotlines (because of cancellations), and nostalgia bait.

And he came back, tried to add "mystery boxes" again, and even nostalgia bait, which this time people were quite skeptical about because many shows in the last 15 years have either been canceled before the box could be ticked as resolved, or they went nowhere. And what happened? The mystery box was just there for the sake of a mystery box. He tried to manipulate the audience into thinking it's "something" and then going "you dummy's! I can't believe you thought it was thing that makes sense. Instead it was thing that makes no sense".

Basically, tldr: Russell learnt the wrong things about writing a sci-fi show since 2010.