I agree entirely with all of your points. There’s valuable info in the titles that is missing from the email summaries. That said, nobody in my community has ever complained about this… but then I haven’t asked them either.
I raised just this point in the (very long and now closed) summary email feedback topic last year, but I don’t think I really got much of a response from the discourse team beyond the general idea that the email summary is not supposed to be the main way that people keep up on discussions. The purpose of the email summary is to drive people to the forum and the huge font in the titles is supposed to help with that.
Interestingly - while reviewing these emails in mandrill, I noticed that the plain text version of the email summaries does not truncate the titles.
Maybe one solution would be to display the rest of the title in smaller font instead of just truncating it with ....
I suspect the discourse team would be open to looking at tweaking the email summaries if they had mockups to look at or even pull requests, but it’s likely not high on their priority list at the moment.