Who would ever trust the built-in seed generation of a wallet? Diceware, write them down, then enter them into the wallet.
Outsource trust carefully, kids!
You trust diceware because you can trust the dice to give random numbers, and the whole process is visible before you. Even with a non-malicious wallet, you have to trust that they competently implemented the random generator and no bugs have crept in over hardware/software revisions.