I don't see Talons of Weng-Chiang as racist. Yes, the villains are for the most part Asian, but that is because they are a criminal Tong recruited by an (non-Asian) ALIEN. The story isn't saying all Asians are evil. Granted, it would have given more of a balance if there had been a sympathetic Asian character, perhaps one of the Tong turned "good" and helping the Doctor.
Casting a white man as Chang is regrettable in retrospect, but that's a production decision, it doesn't detract from an excellent story. It wasn't intentionally racist.
Boring? I find it extremely dramatic, but I guess that's a matter of opinion too. Tom Baker is still taking it seriously, Louise Jameson excels as Leela in an alien (to her) setting, and Jago & Litefoot are much-loved characters who have their own successful audio spin-offs.
...I think myself that you nailed it just here Meglos with there being no 'balance' within the 'Chinese' characters... in the 80's there was a lot of mistrust with the Chinese etc at the time... I think that the writers at the time probably thought that everyone hated the Chinese and therefore played on the public's fears of the 'commies' just to sell the story I imagine... which is a shame really... the writers of the show usually 'get it right' most of the time... the story itself was 50-50 with me at the time although I have seen worse lol!... as you also said... Tom Baker was still taking it seriously at that particular time which did help to take the story more seriously but it still did have many faults... oh well... you can't get it right EVERY time I guess... lol!... oh!... by the way... I loved Leela... cheers.