UPDATE: My first assumption was flawed about Monero. Monero is pretty much fucked, because of its constant Stealth Addresses.
Two payments can be connected together the same way, it’s no different on altcoins, where every transactions are mixed. However the conclusions you can make from that connection is less strong. The scale could go from Bitcoin through Monero, all the way to bank cards, where the bank cards are the most private ones, since no information is shared with the public.
It’s interesting to mention, that the paper says the Lightning Network would be in the same level as the bank cards. Though I suspect there might be different challenges there, who knows.