I genuinely think, only in top level football, people have completely changed the definition of what a headbutt is.
The problem is that he made a headbutt motion and though soft as shit it was still a headbutt motion.
Whether he connected or if it was forceful or not shouldn't be part of the consideration of where it sits in the violent conduct stakes as that's when things start getting problematic with it becoming more and more accepted until people do start getting hurt, see the way holding, grappling and diving has got worse as time has gone on with referees becoming more and more lenient as players push things a little bit further each game.
The facts are pushing your head towards another players face is not a part if playing the game, he wasn't trying to play the ball, he wasn't trying to block a pass, his actions only happened because he lost his temper and was lashing out. That should be the basis of this being a red card, not withstanding the precedents that have been set over this going back decades.
The other big problem with the decision is that it if a player does exactly the same thing in a game between the team in 12th and the team in 13th then the player would likely get a red card and it wouldn't even be a discussion. Personally, I dont think there should be different rules depending on the stakes of a game, the same way that I dont think a goalkeeper should be able to handle outside the box just because it's an FA Cup Final and it's not what the neutrals want to see.
Taylor and Brooks didn't issue a red card as they knew that sending off Gabriel could be a deciding factor in not only this game but also Arsenal's next 3 games, which in a title run in it could easily be seen as the decision which cost Arsenal the title. That absolutely shouldn't be part of their considerations when deciding what is an offence and what isn’t but their lack of action and cowardice could well be the factor that gives Arsenal the title and robs our players the results of their hard work this season.