The Arsenal one was hardly the worst sending off ever, it was clearly a yellow card, possibly an "orange", and granted it's a harsh red, but hardly a miscarriage of justice, the kid made no attempt at getting the ball, and could have done real damage to the opposition player, it's not too different to McGinn's v Spurs last season.
I watched a bit of the Chelsea v Arsenal WSL on Sunday. One of the Arsenal players got sent off for foul and abusive language. Think it was a straight red as well.May the PL should take note.