Saruman also blocks Rowan's military assistance to Gondor

Well... depends on whose account of the War of the Ring you read:

Eskov bases his novel on the premise that the Tolkien account is a "history written by the victors".[2][3] Mordor is home to an "amazing city of alchemists and poets, mechanics and astronomers, philosophers and physicians, the heart of the only civilization in Middle-earth to bet on rational knowledge and bravely pitch its barely adolescent technology against ancient magic", posing a threat to the war-mongering faction represented by Gandalf (whose attitude is described by Saruman as "crafting the Final Solution to the Mordorian problem") and the Elves.[2]

(The Last Ringbearer)