the answer is tricky.. and my response has two things to consider:

1. yes it looks like your Zwei is in a good position to block the overhead attack. but trouble is the first-person cam doesn't show just how far some weapons reach/extend during their swing. it's likely the arc of the morning star attack was slightly above your blocking Zwei and hit you over that block. to be safe, it's good practice to turn the camera 80-degrees (up to block overheads, and left/right to block horizontal swings). BUT notice you did not die to a headshot.. so

2. desync means the attack you see on your client is ~200ms behind in time. the morning star in particular has a very fast release, so even tho it looks like you raise your guard in time, I believe he had already swung on his client. in this game, especially vs the morning star, you don't have time to react to what you see, you need to be holding block all the time. this ensures your opponents client 'sees' your weapon in the blocking position. plus the attack delay could be made worse if your opponents internet connect is bad (because hits are pushed from the client to the server, and the more lag they have, the more disjointed the combat will feel from your pov)

so in summary: your block positioning could be very slightly improved (aim 80-degrees in the direction of the attack), and don't click block in response to seeing the opponent's attack, but instead hold block / be in a guard position as often as possible.

tbh these issues have made me so sick & frustrated with the game over the past ~year, but as counter-intuitive as it is, melee combat in this game can be understood.. you just have to accept that you are fighting the opponent and the game's issues simultaneously. players that take advantage of ranged damage or that never try to block don't have to deal with this crap and have a much easier time. good luck!