Well, it depends. I still have to have some way of passing on my time-locked transaction to my heir. I can simply give it to them, knowing that they won't be able to use it unless I die or are incapacitated and therefore are unable to invalidate it, but they can still look at the transaction and see how much bitcoin I am holding and on what addresses. Or I have to update my will every year with a new timelocked transactions which is time consuming and would cost a fee. There is the problem of me forgetting to invalidate it or not being able to access my wallets in time (in jail, in hospital, wallet lost/damaged/destroyed and I can't get to my back ups in time). You need to be entirely confident that the recipient of the timelocked transaction is not going to lose access to the address it is sending to. There is also the problem that I cannot spend any of the coins in that timelocked transaction without invalidating it, so my daily spending bitcoin is not included in the process. An encrypted seed phrase gives away nothing about your holdings, does not need your ongoing action to keep it safe, can be sent to any address once recovered, and can cover all the coins you hold including ones you are actively spending.

There are pros and cons to both approaches.