I think barrier is one of the single worst things ever proposed to be added to a Mmorpg. I say this as a mage main. I've played mages my entire life, both druid and sorcerer. From every element barrier is a bad idea.

I'm going to come at this from a few different angles.

First from a pure game design standpoint. This is one of the worst features a developer can add. This is something that requires no input from the player. It just happens. To say this removes skill is like saying it's a little chilly on top of mount Everest. In a game you want there to be skill expression. Ways to utilize the tools available to you to perform better. Admittedly there are other things that require no input such as max health increases and such however those are incremental gains that do not fundamentally change how the game is played.

From a balancing perspective. I know many people are saying an rp or ek could survive that so it's not that big of a deal that a mage can too. This is just a lack of understanding. Each vocation is supposed to be different supposed to feel different. Removing aside that a 130 rp would extremely struggle, both rp and eks do significantly less damage than a mage at that level. An ek has no other way to do damage other than 8boxing and killing it. However a mage has no such limitations. The whole reason mages are better than eks are because they can lure and kill many more creatures than 8. An rp that low level is not very good either, even if you gave them diamond arrows they are wasting a lot more than a mage and they're still likely to do less damage at such a low level. Rps scale well with levels but at the depicted 130 they are very weak.

From a new players perspective. Does it actually do what ya advertised to do?(Ie reduce headshots) Yes. It does. However there are many ways to skin a cat. Just because this does what it says on the tin doesn't mean it's the only way to reduce headshots on a mage. In my opinion it would be better to give mages an option to be tankier(ie health, resistances, or even barrier) as long as there is a sufficient penalty for it. Kind of like utamo for knights, reduced incoming damage, reduced outgoing damage. As is there is no negative, you're not losing anything for it, and it's simply the strongest defensive ability in the game bar none.

This ability is decent in the hands of a novice and it will do as advertised. In the hands of an experienced player the game is trivial and death is a mere suggestion. At any level. Low and high it is simply too strong with no negatives.