From OOC perspective, yes this is done to make Hedge Wizards less powerful than Hermetics. Lorewise it is justified by a lack of Theory & understanding behind their powers, or a lack of development. In latter cases, it is a flaw that can be overcome with research.
Spoilers for Dies Irae - Twilight of the Gods: Your idea is one of the consequences of a successful Ragnarok: for the Gifted practitioners who manage to link themselves to the Golden Chain, Difficult Arts become regular Arts and standard Supernatural Abilities become Accelerated.
That being said, I think that making Accelerated Abilities into regular Abilities for the UnGifted is a bit much and would go a long way to further cripple Hedge Wizards, rather than make them more powerful. A lot of Hedge Traditions have a lot more UnGifted practitioners than Gifted ones. Some example Abilities that would be severely impacted are Sihr, Warding, Banishing, all the Goetic "Arts", At least, they're the first that come to mind. There aren't all that many of them that are accessible to the UnGifted, granted, but it just makes things even harder for ones that do. UnGifted Sahirs already have their magic limited to the Might of a Spirit they can summon. A crippled summoning ability of any variety would instantly cut The Order of Solomon down from a "potential threat" to a laughable obstacle. Part of their strength comes from the sheer number they have over the Hermetic Magi.
In my humble opinion as a Hedgie enthusiast, Hedge Wizards already have a potential to pose a threat to a Hermetic Magi, providing they can play to their strengths.
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Folk Witches can ignore Parma Magica altogether with their Shapeshifting, which grants them both combat-worthy forms (bear, lion, wolves, etc.) as well ones more suited for spying and assassination (birds, asp serpents...). Their potions can reach decent Penetration totals even without having an AC to their target, now you just gotta make them drink it...
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Gruagachan shapeshifting is criminally easy compared to Hermetic Muto, they can grant new virtues or bolster their martial prowess to cut you down mundaely. Or they turn into giants and chuck boulders at you. Unlike Hermetics, they don't have to be able to perceive you, so in theory they can shout at you in total darkness or from the other end of a scrying tunnel, and you will still be affected. Hermetics don't have that luxury without additional intellego spells or other means to perceive their enemy.
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Vitkir can perform natural changes and make among the best supernatural killers out there. Their flaming sword for example is completely natural, and no amount of Parma will save you from it. They can also ward themselves against most elemental relatively easily, safeguard their minds against Mentem, or bolster their Combat abilities or even just sheer speed so that it becomes very hard to fast cast against them
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Nightwalkers are masters of guerilla warfare. Aegis won't stop them, for the lack of Might. They can pass through solid terrain, steal arcane connections, and spy on you, or just stangle you in your sleep since they can effectively teleport.
And that is just to name a few, we haven't even touched upon the absolute menace that the likes of Muspelli can do. If you give them Accelerated Abilities, ontop of their Trolldomur Multipliers? BOY there won't be a Magus alive who would be safe from their tomfoolery. For reference, they multiply their abilities by a number of modifiers when they use Trolldomur. This can already result in pretty high Penetration. Accelerating it would make them downright busted. A lot of traditions would also suddenly gain a second proper art and so their penetration would end up being on par with the Order.
Yes, your change would grant stronger Penetration overall. As it currently stands they are not entirely helpless either, many just don't specialize their skills in battling supernatural enemies, nor do they care to or are capable of organizing into opposing the Order. Penetration Ability is a must, and most Hedgies would be able to breach most Parmas with some prep - stealing some ACs or shedding blood are good ways to go about it. They are still weaker overall, but should not be underestimated.