MAlexMatt
Banned
I should have been clearer. The situation as it stood is providing very good reason to follow a general over the Senate. But even if you reformed it as PhilippeO suggested, men who are loyal to the general over the republic "for whatever reason" still give him a force to overthrow it with.
Sure, you'd need such a reason to exist, but its not unheard for charismatic generals to inspire their men to follow them "anywhere", and that's a start - and a fair step more than that if the general nature of Roman society doesn't encourage devotion to the existing order as particularly desirable.
PhilippeO's suggestions would actually go a very long way towards fixing the situation so that armies are loyal to the Senate instead of individual generals.
Charisma is one thing. Being the guy who pays the bills is a whole nother thing. In general, having charisma and being the guy whom you depended on for pay and land gave later Roman generals huge amounts of power over the state. Having one or the other was never enough. A charismatic general who nevertheless wasn't the prime source of income, both present and future, for the legionaries isn't going to be able to overcome the cultural inertia present amongst the general populace.
Even as late as Sulla, a group of his officers refused to enter the city the first time he took it by force of arms from the Marian partisans.
I should note I don't see it as inevitable - something going horribly wrong, yes. The end of the republic as it happened OTL, no.