Thank you!
That’s what I plan to do in the future, once the big import has worked, for all subsequent emails.
Looking at it with more calm, I actually see two more differences. To quote @mdbraber who wrote the script, there are at least those advantages over the inbuilt solution:
The backlink being what made me write this post in the first place.
In addition, if the Python script mentioned here Separate imported e-mail attachments for better search - #4 by mdbraber still works, then I can also remove the attachment from the eml and save space by replacing all the duplicates with replicants.
However, I don’t know if the abovementioned scripts still work in DT4.
Edit: there’s a new version of the script, which @AWD seems to have made compatible with DT4: