Why? Is this just a matter of your believe or you have the strong evidence for it? As it have been said in my above post the only thing that matters is the private key. Can you prove that private keys generated from BIP39 SEED lack something compared with those priv keys obtained from native Electrum SEED?
As said above, there is no difference to the derived private keys as long as the cryptography's method is strong. Why we do analyze this is because of the checksum and probably because of the fact that generating entropy from electrum is much more random than a
github page. The checksum, if you're unfamiliar with, is bits representing the sum of the correct bits. The last word of every seed phrase is affected by the checksum. On a BIP39 twelve-words seed, that requires 4 bits checksum, there are on average 2048/(2
4) = 128 different combinations of valid seeds. On an electrum seed, that requires 8 bits checksum, there are 2048/(2
8) = 8 different combinations of valid seeds.
This means that if you ever need to brute force your seed, you'll finish you search 16 times faster.