I think these mints have a purpose for trusted relationships. Like if you’re part of a group of friends that regularly do things together it would make sense to have a mint for fee-free exchange. Similarly, you could run mints for your household cash exchange (privately teaching your kids about digital money), if you find like-minded families you can exchange mint-to-mint via LN privately also. Federated mints would have more utility - you could have regional networks of like-minded people exchanging value privately. Think like a homeschool event network or something like that.
You could use LN for those cases but you have to pay fees and lose the privacy add from the mint