A safe assumption is that until a game developer makes a statement on something regarding gameplay, it is still considered legal. For now, the fact that it remains in the game and no comment has been made means it can continue to be done. If BB came down tomorrow and said "No, don't do that" and removed it through some technical programming that we will not be privy to, then so be it. For the time being, however, it remains a topic that they have not spoken out on, and so it will continue.
The ToS states that you cannot use a bug to your advantage. Here's the question: Has it been defined by the developers as a bug? As far as I can see, it hasn't. The group of people who are using the blocking technique to their advantage do not see it as a bug, while you do see it as a bug and therefore do not use it. So, for the time being, let those who don't consider it a bug to continue using it, and you can continue to not use it.
If BB comes down tomorrow and says, "You are not allowed to do this", the people who truly care about enjoying this game will no longer use it, and will adhere to what BB says.
The main goal of this forum is to help the players. Asking a question to the development team would be a more appropriate course of action. Asking us, as the players, whether or not it is a legal move does not matter, as our opinions do not hold any weight against the developers. You are getting opinions here, such that some people do not like it and don't use it, while others don't see the harm in it and continue to use it. So, let it be that for now, until BB makes a decision.
(As a personal opinion and side note, stating that having accurate timing is exploiting a bug means that a lot of players, such as myself, would be exploiting bugs in games such as Kingdom Hearts 2, where a lot of battles require accurate timing to make things easier through reactive commands. If I hit the button right when I'm supposed to, I do not agree that constitutes going against the ToS just because it's accurate timing.)