"hardly sensible" is correct and usable in written English.
You can use it to emphasize something is not sensible or logical. For example: "She was hardly sensible when she decided to quit her job without a back-up plan."
This is hardly sensible or sustainable.
And not checking your bank account regularly is hardly sensible either.
Liberals may have thrilled as Mr McCain told the religious right where to go, but this was hardly sensible politics in a party in which evangelical Christians make up half the primary electorate.
(Whether Moscow's definition of fighting the Islamic State is the same as ours is a separate issue: Aleppo should not be forgotten). But for the West to give away something to reward Russia for action that it is ready to do anyhow is hardly sensible policy.
Whether or not the chlorinated hydrocarbons are the primary cause, it seems hardly sensible, under the circumstances, for us to expose ourselves to poisons that have a proved ability to damage the liver, and so, presumably, to make it less resistant to disease.
The question of whether or not it is true is hardly sensible.
But given the government's incoherence and evasions and divisions about Brexit, it is hardly reasonable to expect sane and sensible public policy anywhere else.
Masoud Golsorkhi: While the Holocaust conference was hardly a sensible idea, it would be totally off the mark to say Iran has institutionally anti-semitic policies.
That hardly seems sensible in a world that's growing more complex and is increasingly shaped by a diverse cast of players, be they new or emerging states, global corporations, criminal networks, or armed groups.
Irrespective of your position on the euro, further European integration, or the rapid reaction force, it can hardly be sensible, or helpful in convincing the public of the merits of the EU, to bring court cases against a greengrocer for selling a pound of bananas.
