"potentially less" is correct and usable in written English.
You can use it when you want to suggest that something may be less than expected. For example, "The project could potentially take less time than anticipated."
"It's potentially less toxic".
Even Himalayan balsam, that aggressive coloniser of riverbanks, seems potentially less lethal than was once imagined.
If systems can link up and share data, they're potentially less secure.
"They should have looked into potentially less expensive ways of doing that".
"They are potentially less divisive than some of my other concepts".
Arts and humanities degrees could become more expensive and potentially less popular under Browne's proposals.
But its government faces a potentially less compliant opponent in the Muslim Brotherhood.
Now the place the troika is flying to seems potentially less frightening, if still hardly Utopian.
There is a potentially less expensive alternative on the Sprint network.
That means a smaller crowd and, at least, potentially less energy.
I suppose it is potentially less embarrassing than getting the name of your beloved tattooed across your bottom".
