Darth Sidious was the culmination of the Sith Grand plan, finally completing the goal that began with Darth Bane a thousand years before. He was the peak of Dark Side power and used it to claw his way to the top of a Galaxy that was divided. But these ancient Sith Lords in their spirit forms, like Darth Revan which we saw in the Clone Wars deleted Scene, Darth Bane and Darth Momin would have absolutely hated the way Sidious conducted himself…

The First reason that the ancient Sith would have despised Sidious was his utter obsession with the Jedi Order and wiping them out. From a very young Age, Sidious already developed a strong hatred of order for many reasons. He believed that they were arrogant, blind to the struggled of the Galactic Citizens and far too self-righteous. It was this hatred for the Jedi that pushed Sidious deeper into the Dark Side than he had ever gone before and it made it his sole goal to destroy them.

Ancient Sith Lords though thought so little of the Jedi Order that they barely even considered them. They would have considered Sidious’ obsession with a useless order of Light siders to be weak and detrimental to his own power. In the end, we know his obsession with the Jedi was ultimately his downfall, and a fallen Jedi returning to the light took him down…

Now the other reason that the Older Sith beginning with Darth Bane would have hated Sidious was his disregard for the Rule of Two. This really started with Darth Plagueis before him, but Sidious continued the tradition by allowing his apprentice to have their own apprentice also, breaking the rule of two. Sidious and Dooku tell themselves that Ventress is only a Sith Acolyte, but come on we all know that he doesn’t care about the rule of two. Pure copium. Not to mention, Darth Maul was taken on when Plagueis was still alive, so there was no regard for the rule of two at all by then…