It is true that there are some flaws with Shamir Secret sharing scheme, especially single point of failure, but it is still fine to use it if done correctly.
You could always generate new account and just add passphrase for more simple way of protection, or use multisig if you like real security with more complexity.
Then send and move your coins to newly generated address.
Is it possible to revert from a Shamir scheme to a typical 12 words seed?
You might want to take a look at this Trezor's wiki page to find all information you need about Shamir Backup:
https://wiki.trezor.io/Shamir_Backup