'less challenge' can be used in written English in certain contexts.
For example, you could use this phrase when discussing how a certain situation presents "less of a challenge" than it could have. "Before we started the project, I was worried it would be a challenge, but it has become clear that it is less challenge than I had feared."
It also offers less challenge than some of its predecessors: everything is a little more obvious and the puzzles rarely have you searching for very long.
As with the use of torture, the use of secret intelligence outside of the ordinary legal process makes it difficult even to discover the violation, much less challenge it legally.
After its first losing record in 40 years, North Carolina entered this college basketball season unranked and unappreciated and was not expected to reach the upper echelon of the Atlantic Coast Conference, much less challenge for a fourth national championship.
Where most students experience this level of challenge daily, highly able children for whom the regular curriculum holds less challenge may not... we must find a way to ensure that gifted pupils enter their ZPD.
Thus there is no suggestion of sending peacekeepers into Somalia again as part of the plans to create a new government, though Somalia presents less challenge for cohesion than most African nations: Somalis share a common language, religion, ethnicity and nomadic culture.
Although the volume of business activity in the field of residential interiors continues to grow, there seems to be less need and less challenge for the professional designer, with the result that more and more of the qualified professionals are involved in nonresidential work.
Furthermore, second half comps are less challenging.
His later work was less challenging.
And the newsstand is no less challenging.
His son, however, never interrupts, much less challenges, him.
Sectioning may become too easy, a little less challenged".
