Equal in the sense that it is representative. Would you say any of the above points prove bias on the part of the bbc?
The BBC have no choice regarding the time given to the PPBs, just as they have no choice oh what points, and with what vehemence 'experts' speak when asked to provide comment on the issues of the day.
The point you make on climate change advocacy, I agree with you, but without the opposing viewpoint, do you think that the bbc would be seen to be unbiased? Quite the opposite. They would be seen as a left wing mouthpiece, because the left wing traditionally care more about that subject.
Same with the cbi and the right wing.
They are damned if they do, and damned if they don't. I don't, however, think trying to find alternative viewpoints, regardless of popularity shows inherent bias. Challenging a viewpoint to test it's rigour is, in my understanding, journalism.