And where exactly did Dropbox make a legally binding agreement with you that allows you to sync 20GB to an unlimited number of devices for perpetuity? The agreement you're referencing doesn't exist.
We are civilized people and don't need to shove contracts in each other's faces for everything. Somehow we have gone from being too violent to too litigious. Not bad compared to violence, but can be better.
Of course there’s no legally binding agreement. It’s still a shitty move to renege the conditions of an existing account.