Liddell Hart's writings were terribly biased as were Alan Clark's. The latter's being absolutely hammered by his contemporaries and his superiors:

"John Terraine and A. J. P. Taylor wrote damning reviews and historian Michael Howard wrote "As history, it is worthless", criticising its "slovenly scholarship".

"Professor Richard Holmes made a similar complaint, writing that "Alan Clark's The Donkeys, for all its verve and amusing narrative, added a streak of pure deception to the writings of the First World War.   Its title is based on 'Lions led by Donkeys'. Sadly for historical accuracy, there is no evidence whatever for this; none. Not a jot or scintilla. The real problem is that such histories have sold well and continue to do so. They reinforce historical myth by delivering to the reader exactly what they expect to read"."

"Graham Stewart, Clark's researcher for The Tories noted "Alan wasn't against quoting people selectively to make them look bad"

Alan Clark as a historian was not shy of just making things up when it suited his purpose - so not a very good historian. Even his tutor at Oxford Hugh Trevor Roper thought that.

Clark's book deals with a very specific part of the Great War namely the BEF campaign under Sir John French in 1915 - OWALW used it as being representative of the British Army and British Command throughout the entire war, which it most certainly was not.

Liddell Hart's "knowledge" was more than slightly suspect as they reflected the work of others General Sir Ivor Maxse (Infantry) and Major-General John Fuller (Tanks) which makes your opening sentence rather strange:

"Liddell Hart believed that the frontal assault was a strategy that was bound to fail at great cost in lives"

I say strange because the inescapable reality of the situation on the western front was uninterrupted lines of trench works running for ~400 miles from the Belgian coast to the Swiss Alps. If they were to be attacked it could only be by frontal assault and starting from 1916 onward the British and Commonwealth troops and their Commanders got better and better at it - Fuller and Maxse being two of them. The 100 Days Offensive fought under the direction and command of Haig in 1918 remains to this day to as the best offensive operation ever undertaken by a British Army. Haig was perfectly correct in his assessment in 1916 that Germany could only be militarily defeated by the Allies on the Western Front - nowhere else.

Liddell Hart advised Chamberlain and advocated appeasement - had Liddell Hart's view been adopted by Lloyd George in the First World War then Germany would have overrun France and won the War as there would have been no BEF in France at all. Mons and Cateau would not have happened the Germans would not have been delayed and the Marne would never have been fought.

A good illustration of this "military theorists" judgement was given early in 1944 when Basil Liddell Hart prepared and distributed a treatise titled "Some Reflections on the Problems of Invading the Continent" Which caused a gasp in the security services at the time.

Liddell Hart was WRONG in 1917; He was WRONG in the 1920s and 30s; He was wrong in the 1940s.