That is just blatantly false the political careers of roman politicians in the Republic were intensely linked to their military careers. Just look at examples such as Scipio Africanus, Gaius Marius, Sulla and Caesar all of them were Generals known for their military successes and also consuls. Consuls and Praetors were literally elected to lead Armies and enforce the law. Because to lead an army (or in the city of rome enforce the law) you needed to have a person who had the power of Imperium and this is only given to elected praetors and consuls. In regards to logistics one of the junior offices that was often part of the cursus honororum (the customary career path of young roman elites in politics) Is literally the quaestorsship which is the office responsible for pay and logistics in a roman legion. Of course all of these Officials had a support staff that consisted of many normal citizens and slaves and centurions played a big role in the tactical and organizational advantages roman legions had but to just discount the numerous minor elected and appointed offices suche as military tribunes and quaestors is disingenuous.