I think I can see where you are coming from. But I can also see where those statements will cause confusion.
For any particular combination of race, job, and level, your stats will be the sum of your race stats at your main job level, you job stats at your main level, and half the support job stats at its level. So overall it's 44% race, 44% main job, and 11% support job. Looking just at the race stats at level 35, you would see:
Hume: Level 35, 268 hp, 112 mp, 14 Str, 14 Dex, 14 Vit, 14 Agi, 14 Int, 14 Mnd, and 14 Cha.
Mithra: Level 35, 268 hp, 112 mp, 13 Str, 22 Dex, 13 Vit, 19 Agi, 14 Int, 13 Mnd, and 10 Cha.
So relatively speaking, Mithra take small penalties to strength, vitality, mind, and a sizeable penalty to charisma, in order to get a sizeable bonus to agility and a huge bonus to dexterity. Now you must also remember that each of the basic stats (besides HP and MP) affect part of your character. Str goes into attack, Dex into accuracy, Vit into defense, Agi into evasion, Int into magical attack, Mnd into magical defense, and Cha into NPC reactions.
Now if you only compare the stats "important" to particular jobs, it would seem in most cases the increase in accuracy and evasion "outweigh" the decrease in defenses and physical attack. All the strength in the world won't help if you can't hit, and you don't even have to worry about defense if you can avoid attacks entirely. Or, so popular opinion goes. But when it really gets down to it, the price for Mithra's superior abilities is paid for with luck. The charisma penalty means that Mithra aren't trusted in "normal" non-adventuring society, which means they need to do more to be accepted. And the other penalties mean when things go wrong, they tend to go spectacularly wrong.
But these differences are minor, and almost trivial. Be who you want to be and you can't go wrong.