They are clearly the market leaders in terms of online btc wallet. What are the alternatives?
They are the online alternatives to the original Core wallet,I don't know why would you for an alternative of an alternative.
that is the weirdest definition that anybody has ever given for blockchain.info!!!
they are actually one of the worst wallets of all times. there have been bugs that led to money losses (for example usage of random.org for their random generator when creating a new private key!) and they have had lots of bugs, also they had the worst fee estimations which usually gave 100 sat/byte no matter what!
and they have not yet implemented SegWit after all this time!