Also these donations are anonymous (to the public) so it's even more egregious that the opposition leaders have not managed to make this into a larger issue (maybe it benefits all parties?).
Incorrect. The opposition in India has been largely castrated, mocked and vilified by media sources in most of the country, especially non-English media.
For the record, I read somewhere that the current Indian ruling party is the wealthiest ruling party in the world with an AUM of $3B (this is an outdated number btw). Meanwhile the opposition has barely enough money to fund the construction of its own headquarters.
Foreign funding of political parties is equally if not more dangerous than foreign funding of news media.