Thanks, I didn't know about the Received column. However, for all my emails, including the backdated ones, this column shows the same (spoofed) date and time as the Date column. (Tested with Thunderbird 68.12.1 on macOS.) (And if it worked, why not make this column the default? And if Thunderbird already determines the received date, why not show it in the message view as well?)
For me, this issue is serious enough that it had to be your call to disclose it, not mine (especially given that Thunderbird's behavior deviates from what other mail clients do for presumably good reasons). The only reason I reported it was to let you make this decision, which you now did.
The thing with scams it that they just have to work a tiny fraction of times to be worthwhile (and cause a lot of damage for the people who fell for it). Only a fraction of people use Thunderbird. But among Thunderbird users, I'd expect that a majority doesn't know about Received headers and how to check them.
Given how little effort it is to address this issue, I'm a bit surprised by the "won't fix". I respect your decision and don't care much about it, since Thunderbird is not my main mail client, but if protecting its users isn't Thunderbird's main value proposition, what is it? (No answer needed.)