It sounded like you lament transition the from Cantonese to Mandarin and you make it seem like a bad thing, near equivalent to the loss of rights and freedoms. I don't feel that way.
Sarcasm aside, Spanish is not easier for Chinese people since barely anyone speaks it in Asia other than nouns in the Philippines. Mandarin is easier because it's already the primary language for most Chinese people and not just the mainland. It's also generally easier to speak and understand compared to Cantonese. Having one standard language is an advantage vs having a million "dialects".
There are many bad things about the HK handover. Standardizing on Mandarin is not one of them.