I have the opposite idea about Marius as person: he was worse than Sulla and he was the direct responsible of the start of the fall of the Roman Republic. If Marius had NOT tried to steal from the rightful Consul the command of the expedition against Mithridate, violating practically every laws of Rome, Sulla would have NEVER marched on Rome and if Marius had NOT attached Rome just after the departure of Sulla, killing or forcing to exile many friends or relatives of Sulla, the latter’s reconquest of Rome and Dictatorship would NEVER happen…Marius is such a fascinating and seemingly contradictory figure; only marginally better, sure, but definitely better than Sulla, but ultimately it's arguable his exploits were even worse for the Republic in the long term. IMO he probably owes most of his whitewashing to his association with the most famous military reform of the Republican era, with his more problematic politics consigned to a footnote to his military exploits.
That was NOT something who Marius had done… the last who tried to do it was Drusus and he was closer to Sulla‘s party than Marius‘.Also the fact that the OTL free reign of Sulla and his crew really set in motion Catiline, the Triumvirates, kinda the whole death of the Republic. Even if Marius was an absolute garbage human being (which he kinda was), actually getting a few Populares reforms through addressing the collapse of the smallholding farmer and the swelling of the urban poor would be huuuuge in potentially preserving the Republic without attaching an Emperor to it.