the fastest way for both parties is over the phone ASAP rather than through a bunch of emails
I don't disagree with your statement, but I read the sentence: "Would you be interested to hop on a call with us to talk about this further?" with a similar gross reaction as the OP comment did.
Reading that in response to Marsf's original message of airing grievances and feelings of disrespect towards his work felt entirely tone-deaf and corporate in nature. Especially in context of this being in response to the Japanese team, where Japanese business communication norms are often at odds with the American standard.
You might think that this method of communication is inefficient, but the heart of the matter seems that the Japanese team finds the very emphasis on efficiency as disrespectful when it comes at the cost of the human element of respect.