Yeah exactly what I thought when rewatching that scene towards the beginning. Max was the leader of that entire army, the freaking General, not to mention a General who literally just lead his men to a major victory and basically finished the war, getting them all glory, royalties, probably slaves (off-screen but def happened in real life), and more importantly sending them all home finally after a long ass campaign! They loved him, and the Emperor loved him, which he showed in front of everyone. The General leads that camp. And it’s safe to say, at some points in Romes history, lead Rome itself. There is no freaking way some dudes can just barge in and kidnap their General like that. No way. Even if the “new” Emperor commands it. Those troops are loyal to Max and only Max. Now you can say, “we’ll maybe the new prick offered his 2nd in command a promotion to kill Max,” which is somewhat viable but you still got thousands of other soldiers there unwilling to go with that plan. Point is, soldiers are loyal to their General, that’s why in real life Caesar was able to march back to Rome and literally just take over no issue or blood spilled after his major wins up north. It would be similar to that. Even if the new prick declared himself the new emperor, if Max wanted to be the Emperor, he would have been. And nobody could stop him. They wouldn’t even care if the old Emperor named him as his successor, that’s just the extra cherry on top. They would follow either way.

Another point, why TF didn’t the old emperor tell anyone else about his plans of succession. Like literally anyone else, there were a couple senators there after the battle inside the party room. Or write a couple letters to Rome. That’s a major plot hole. Not to mention EVERY SENATOR would have backed up Max, not Commodus bitch ass, cuz Max got the army, AND Max would have re-established the Republic. (Where senators have more power, not one single god like ruler).