I have to say that in e.g. https://lkml.org/lkml/2018/12/22/221 he is extremely polite compared to 1 year ago. Of course it may sound harsh to some but I can see him trying.
I think that mail is entirely positive for the Linux kernel users. Clear unequivocal language expressing the policy and stance of the project. I can’t see any reasonable way to temper the harshness without removing a key element of the message.