Clan characters get bonuses based on their much harsher living conditions and tendency to begin training for combat roles at the same time Spheroids are typical learning to read. But even then, there are drawbacks that CAN be bought off (to provide for superlative examples like Aidan Pryde and Natasha Kerensky), including Slow Learner (which is an effect of their limited academic options, compared to those in the Sphere).
The Field Aptitude issue applies only to Trueborns (or freeborns born directly from Trueborn parents, if a GM wishes), which reinforces their genetic breeding for a specific combat role, and even then it generally applies to the role the warrior's phenotype was meant specifically for. Because it takes several generations to perfect, and relies entirely on the presumption that the Clansman's role will fit the one for which he was bred, this can turn out to be useless if the warrior "washed out" into a different role--such as Aerospace Phenotypes who become ProtoMech warriors, or Elementals who become Tankers/Cavalry. This can be further illustrated by contrasting the rules found in Era Digest: Golden Century with those in the core book. In ED:GC, Clan Phenotypes do NOT gain the Field Aptitude effect until 2900; any Trues born before that date receive a much watered-down set of mods.
Overall, though, the goal of a Trueborn Clan character is not necessarily to balance them against Spheroids. The Clans spent centuries breeding themselves for superiority, while the Inner Sphere was not nearly as focused on eugenics and weeding out the chaff from the wheat. Still, with the exception of the Field Aptitudes, the numerical values of the AToW chargen system should give any two characters an equal chance for greatness as long as they start with the same amount of XPs.
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