> It's unlikely that someone will make their paraphrase long enough to prevent someone from brute forcing it

Reality check: for the casual user that doesn't have a life changing amount in Bitcoin, it is more likely that the seed is found by a roommate or some random guy that works in their property, instead of being the target of a determined, informed and well-equipped attacker.

So even a medium simple and high memorable passphrase can be effective in many situations as additional security layer.