remains unfailingly readable, if not wholly reassuring

[ida2]

In the context below, could you please explain the bold part?

By contrast with the highly complex and explosive styles being developed on all sides, the measured cadences of his writing proved mildly and agreeably surprising. It was as though fluency, clarity, and simplicity, the patron goddesses of the average man, had returned to earth. Those who prefer the sort of writing that gives them pleasure without requiring much thought took an immediate fancy to his work, whose seductive charm lay in its totally unaffected appearance, whose limpidity sometimes allowed a deeper thought, but nothing to mystify: his work remains, however, unfailingly readable, if not wholly reassuring.

Source

 

[grassy]

His work remains unfailingly readable and it may even be wholly (= completely) reassuring.

PS That's quite a clever way to politely insult a writer. Kudos to the author of the passage.

 

[Toby Sherman]

The contrast is between his style and his subject matter. His style is very clear, even if what he says about his subject (politics? public health? the likelihood of nuclear war? If you name the author, we might figure this out) may cause us to feel some amount of discomfort.

 

[Edinburgher]

and it may even be wholly (= completely) reassuring

It's ambiguous. Sometimes "if not" means "or even", sometimes it means "but not".
I think here "if not wholly reassuring" means "even though it is not wholly reassuring."