My biggest issue with this set up is you are essentially reducing the entropy of your seed phrase to the entropy of your KeePass encryption key. A 24 word seed phrase has 256 bits of entropy. The average human generated password has an entropy of around 44 bits. Even if you draw from all 95 printable ASCII characters (lowercase, uppercase, numbers, symbols), and generate a truly random encryption key, a 12 character key is still only 79 bits of entropy. You would need 39 characters to equal the entropy of your seed phrase.
From quick research, it looks like a typical key derivation from seed uses only a little bit of key stretching, while KeePass and other managers use very big amounts of key stretching and they constantly keep it up to date to match the modern brute-force capacities. So, even though this method reduces entropy, it still has comparable difficulty of brute force, as long as the password is good.
You're right though that an unexperienced person can shoot themselves in a foot by forgetting their password or having a very weak password.