To answer your questions you have to understand how ethicalconsumer.org do their rankings. Recognising that different people have different priorities for ethics, they provide an interactive way of weighting your interests (Environment, People, Animals, Politics and Product Sustainability) and therefore adjusting the overall scores. The default option is with all these weighted equally.
Assuming that scores across categories can be compared fairly (I think they can); Triodos is a the top of the list. Of the ones I previously mentioned Nationwide is next, then Monzo/Revolut/Tandem/Starling (equal score) and The Co-operative Bank is lower down. To be clear, there are other banks and building societies between and equal to the scores of Nationwide and The Co-operative Bank, but I don’t want to upset ethicalconsumer.org by quoting their table more fully as their service is subscription based (free trial available though). All of these fall in the top fifth of the table.
As already mentioned The Co-operative Bank was never a co-operative/mutual really, and was often marked down due to activities of The Co-operative Group. It was felt that political campaigning was a negative feature (regardless of political persuasion), and the animal farming of the Co-op was previously cited too. So it is clear activities of a parent group do figure in the scores.
However, since the Bank has been owned by hedge funds, the score has gone up somewhat (even though it is marked down because of their use of tax havens). The Bank’s ethical policy has been strengthened under their ownership. There is a comment in the best buys that The Co-operative Bank is the best of the group after Triodos (which is the recommended best buy), and a further comment that app banks are worth looking at.
I would say that Monzo is in a special position at the moment given its relationship with its customers and investors and it will be interesting to see how the business develops. I’m not pushing Monzo here particularly, I am a fan of mutuals and particularly credit unions (my local one is about to introduce a “proper” debit card linked to accounts) and I’ve only had my Monzo account 8 days. However, it does strike me that Monzo could do a lot of social good, and I hope it will.