If the Clancies are going to be different, one of the things they should have is massed combat vehicle formations, with mechs forming a supporting role, like the Hells Horses. They don't think Mechs are inherently superior to massed combat vehicles. Plus, if a general is being engaged in combat, they’re either having a really bad day or they’re insufficiently focused on their duties as a commander.
To explain why Mechs have such a mythos in the IS, consider that the wheels were coming off all the nations in the tail end of the 2nd SW - mass famine and epidemics, civil unrest, breakdowns in communication and administration, mutinies, entire worlds falling into warlordism. At the absolute nadir of the Succession Wars, most governments were becoming far more fearful of the threat of domestic revolt than foreign invasion. Ultimately, conventional forces were largely permitted to be expendable. It was considered far easier to observe and maintain the loyalty of an extremely limited number of mechwarriors than mass formations. Aside from a limited conventional auxiliary force, the main garrisons on worlds consisted of paramilitary gendarmes with no weapons heavier than machine guns and mortars - enough to keep the locals in line without posing a major threat to regular military units.
Over the ensuing decades, the central governments of the Successor States painfully, agonizingly, rebuilt their legitimacy and stabilized affairs, bit by bit. The general increase of conventional military forces and of combined arms going into the early 31st century reflects these shifting circumstances, something that the new mech aristocracy was well aware of. The reactionary Warrior's Cabals in the Federated Suns would be the best example of this - seeing in the ongoing military reforms a diminished future, one that would inevitably lead to their ultimate marginalization as an independent political force, they plunged the Federated Suns into a multi-year civil war.
