I think the secret for me was to not compare to the others you mention, all of which are favourites. I found myself listening to them almost as if they weren't John Martyn albums and therefore not freighted with the attendant expectations. I also think that the bands and arrangements can sound very of their time, and therefore dated, but again I tried, and largely succeeded in hearing them with fresh ears.
I'm not sure how much sense this even makes and it was achieved after 30 years of largely disregarding them. Perhaps that distance helped.
'One World' was my entry point, and played endlessly at the time so always sat on the right side of the divide for me.