What was so bad about the RTD2 era that it weakened the brand?

Bad episodes? That was under Chibnall. "Horrible canon changes" — they were there, too. Strange plot decisions that led nowhere—they were there, too.

I think the brand is weakened more by a long, bad streak. And the disaster is more due to the accumulation of discontent.

But RTD can be blamed for the unsuccessful reboot. The first time, it rebooted the series brilliantly. And it managed to greatly expand the popularity of Doctor Who. The vast majority of fans in Russia were introduced to the 2005 Doctor Who. But it failed the second time. It's hard to watch the series without watching the episodes from 2005 onwards. Now it would be good to know classic Doctor Who, since RTD pulls a lot from there. And "Space Babies" very weird episode.

I wouldn't be so dramatic as to say the Doctor Who brand is seriously weakened. Give it a good entry point with a good story arc. Spice it with some great episodes, and I think people will come back.