I visited Finsbury Park station in July 2019. It gets an accessible rating on the TFL map.
All the London railway stations :
Finsbury Park station
Finsbury Park is on the Piccadilly and Victoria underground lines and the First Capital Connect rail network, and is now accessible to wheelchair travellers. See pictures and further accessible transport in London detail from links below.
Finsbury Park platform is raised at certain sections to allow step free access to the train
Finsbury Park lift at platform level
Underground lines : Piccadilly, Victoria, National Rail First Capital Connect
AccessAble Access Guide :
Accessibility friendly : Yes it is.
The National Rail station has partial access, which includes being able to cross between some platforms, although no ramps are available onto trains.
Finsbury Park underground is now accessible to wheelchair users due to lifts, and raised level platforms at certain sections of the train.
General description : See wiki
More comment : National Rail Guide & Maps
Inclusive Britain Station Guide is probably out of date.