The helmets are obviously supposed to be atypical, and clearly have the stats they do in order to encourage non-magic users to try out magic and take their character in a variety enhancing direction. Think.
Yeah, right, and I've got some ocean front property in Arizona. Thief characters traditionally wear light armor. By coincidence, the light armor helmets improve lockpicking, alchemy, archery, barter, and carry - all skills generally associated with thief archetypes - and regen, which is hardly useful for anyone.
Warrior characters frequently wear heavy armor and want resistances. By coincidence, the heavy armor masks have poison, disease and elemental resistances. There is also a stamina mask, which is generally more in demand by heavy armor users because they use more stamina.
Mage archetypes usually wear no armor (classic mage) or heavy armor (battlemage). By coincidence, the magic-skill boosting effects (other than regen) are on heavy armor. Bethesda could have altered the alteration perk to make these masks useful for both classic mages and battlemages, and made a bad design decision that favors the battlemage.
A 20% reduction in magic regen will not encourage non-magic users to try out magic. Without the perk in a magic skill, a non-magic user would be luck to have enough mana to cast an apprentice level spell, and by the time the non-magic user can kill a dragon priest, apprentice spells aren't going to cut it.