Firstly, you've limited yourself by not including counter argument, which will help hit the 'analytical' bit of the mark scheme. Whilst it might seem like it reduces the consistency of your argument, as long as you constantly link to the focus and explain why it doesn't aid your argument, it can be a good way of getting the top marks.
In most questions, you can see how the examiner is trying to hint at what point they'd put in the answer: the example of barber surgeon could be used to show how there was some progress in the medicine as it became more accessible to poorer people and in some ways, encouraged early investigation of the body. However, you could go on to say how this was limited as barber surgeons sometimes did more harm than good as they created further complications, or just reinforced the practice of bloodletting which did not help progress medicine. This would still be consistent with your overall judgement.
Likewise, you can even group up the points they've given you because a lot of the time, you want your blocks/paragraphs to be broad and a whole paragraph on blood-letting isn't as effective as one that combined barbers surgeons and blood letting and one on the influence of the church and Galen's ideas and another on attitudes, which can be linked to the case study of the Black death like you've already done.
I'd be careful about making claims like 'It led to lots of people dying as these ideas were clearly incorrect and didn’t help in any way.' because Galen's theories hindered the development of medical understanding, and this flawed understanding lead to physicians making incorrect diagnoses, followed by ineffective treatments, which caused increased death. As you can see, whilst it may seem obvious, you have to explain your line of argument clearly instead of rushing to finish your point. This makes your answer more 'thoughtful' which is want the examiners want.
To add more complexity you can even argue that it was more so the church's restrictions rather than Galen's theories that truly hindered medicine as Galen's theories themselves could have at least been a starting point into further investigation but it was the church that prevented this from happening by enforcing censorship.
But overall, your answer is a really strong one and is certainly has a sustained argument throughout. You didn't fall into the trap of story-telling which is great, but make sure you analyse more thoroughly as this is where you'll get most of your marks.