What if Magnus Maximus managed to be the only Emperor of the West?

Recently I have been reading and researching about the Late Roman Empire and I have come across a character that has caught my attention, Magnus Máximo, a Spanish general who rose up in rebellion in Britannia, invading Gaul and defeating Graciano. Although a usurper, he would manage to be recognized as co-emperor of the West together with Valentinian II, controlling Britannia, Gaul and Hispania. Despite this, his ambition would lead to his ruin, invading Italy and briefly removing Valentinian II from power, he was later defeated by the forces of Theodosius I, and later executed.

Despite the fact that he can be seen as just another usurper, it draws my attention to the possibilities that he may have, taking into account that he managed to be recognized as Augustus of the West, maintaining power for 4 years until he was defeated by Theodosius. This has led me to wonder, what would happen if Magnus Maximus had succeeded, becoming the only Emperor of the West? Perhaps defeating Theodosius in battle or perhaps making him more concerned about barbarian incursions or a war with the Sasanians (for the latter the division of Armenia and the Acilisene peace would have to be altered) or perhaps also preventing him from invading Italy . I would like to see his opinion on this.
 
He seems to have been a competent military leader, though it must be noted that all of his successes are due to eventual betrayals on the enemy camp, and he certainly administered Gaul to a solid degree.
He'd find an accord with Theodosius, in all likelihood, but I fear he'd eventually want to try and overthrow him too, or the two would find a way or three to bicker, or some rebellion would surge and he'd find himself betrayed and killed in all likelihood, because that seemed to be a constant among Western Emperors. So not much, I'm forced to conclude.
 
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