> That still lines up with the core tenets of Hinduism, that one chooses one's birth based on the ripe karmas.
Vedas says one is born according to his past life karma.
> The original caste system - the varna dharma - simply means that at different stages of life and different people more naturally express ways of serving society - some are workers, some are business people, some are warriors, some are priests.
If people were allowed to change caste most people would have changed to priestly caste as it is the most easy life one can have.
> A brahmin (priest caste) does not need to be born from brahmin parents
No father would want his child to convert to lower caste.
> The British further abused the caste system and perpetuated this false understanding of it for their own benefit.
I am not saying Britishers came as saviors, but they are the ones who setup schools to everyone, obviously for their own profit ,but still mass education happened only after their conquest.
> This is not the original way. The Vedas actually tell us that castes are fluid through one's life and not based on which family one was born into.
Assuming this is true, who has the authority to decide who should belong to which caste. Obviously the people in the highest caste will decide and they will try to main the power. Its simple as that.