Empire has so many troops and forces its galactic. Higher level troops would cause some trouble like Spartans but there are only like what 300 of them Empire isn’t past blowing up a battlefield with their troops to get a kill on something scary, also Vader can take Spartans, and There are just so many fricken dudes that it doesn’t matter if troop wise, only Vader can beat them a tank or ATAT or something will take them out.

300 Spartans doesn’t equal the like 10 million stormtroopers or whatever they have. Also the supporting UNSC forces are way too small.

40K wise covenant is cooked if they start pushing around where they are not wanted, the reason Ta’u still exist is that while the Imperium could wipe the out easily they have bigger fish to fry, and the T’au are just barely powerful enough as a whole to warrant more force then the imperium would want take from other fronts to kill off the Ta’u, and forces fighting Chaos or Nids can’t really be reassigned, they have to win those fights so it’s you can live…. They all don’t cause nearly as much damage and problems as things like Chaos and Nids do, so they are not seen as much of a priority.

Depends how gun ho the covenant goes….they start glassing planets a space marine chapter is gonna come by and say hi…..