The comparison was not meant to be in terms of custody of the funds, but rather in the fact that you are paying them (the third party).
Eeeh, then a lightning node can also be compared with a bank. You pay for each transaction you make and it is dependent of the amount you're transferring! I considered the 2FA third party's custody as a comparison with a bank which, as I've said, isn't the same.
You can apply the same "logic" in this situation with the coins stuck in a 2FA wallet. Sure, I will lose if I don't sign that transaction and release the funds, but screw you, so will you. You never know what screws someone has loose in his head.
Agreed, you just said that “It prevents one person from spending without the permission from the other”. All I'm saying is that one of those is the owner, so the other has an advantage of cheating since they never had that money before.