I use 12 word child seeds as passphrases for my wallets.
I have never given this much thought, but is there an upper character/word limit in Bitcoin for passphrase lengths? I am asking because you said you use 12 words as passphrases. When I configured my Trezor with passphrases, I noticed that the device has a limit of 6-7 words (depending on the length) It seems it's different wherever you look. It's probably a memory limitation of Trezor, preventing users to set up longer passphrases.
Some hardware wallets have limits. Trezor limits to 50 bytes. Ledger limits to 100 characters. A 12 word passphrase tends to average around 75 characters.
I love using BIP85 to have redundant backups. I still back everything up the proper way: paper & metal, secured in locations only I have access to. But BIP85 gives me redundant backups of everything. And really, once you have more than one seed, I think using BIP85 to create mathematically generated redundant backups makes a lot of sense.
The catch, of course, is that you have to start your entire wallet setup from scratch, because in order to use BIP85 the way I do, you need a parent seed. For me, I felt like starting over with my wallets was a necessity after Ledger announced their key extraction firmware. I didn't feel like there was an immediate risk, but long term, that nonsense is a time bomb waiting to go off. So I started over with everything, from scratch.
On the other hand, for somebody who only wants to keep using the seed they already have but start using passphrases to coins into different wallets (perhaps a trading wallet & a hodl), BIP85 is perfect for generating those, which means via BIP85 the seed protects against loss of a passphrase.