I visited Arsenal station in July 2019. It is not accessible. Stairs, and a steep slope.
All the London railway stations :
Arsenal is not an accessible public transport station for wheelchair accessibility due to the 27 steps to platforms.
Arsenal station stairs (27 steps) from platform
Arsenal station tunnel from platform
After climbing these 27 steps, there is then a long tunnel, the first part is very steep, then finally flattens out. I was not the only person struggling with this slope.
Underground lines : Piccadilly