I think I've come across something similar to what you just said but I still don't fully understand how the whole SLIP-39 seed works. Plus back in the day I still remember that ELECTRUM seeds were considered better than the regular BIP- 39 seeds because of their word list and entropy too.
I never knew BIP 39 seeds of electrum had better entropy. To my understanding
They are all 128 bits for a twelve word seedphrase and boast same entropy likewise SLIP 39(20 words here) .
The only difference is in application
SLIP strength is on distributed security making it harder to steal, electrum just boost flexibility and little less complex.
I doubt anyone would be reading these days because people are more incline on youtube.
Paper method of securing seedphrase is quite one of the best and cheapest when dealing with theft by humans
But one of the worse against disasters.
we should hold necessary backup too, not just one as you said. One for ourselves and one in the place we can reach often and a few in most secured locations that should be accessed only if necessary.
The issue of multiple backups location is that it increases the likelihood of the seedphrase getting exposed.