This is highly debatable. The Mayors of the Palace under the Pepinid line, the ancestral lords of Aachen, were not as assured of their position until the prestige garnered in the victory at Tours and the subsequent following 'victories' in the Aquitaine. It ingratiated the Peppinid line to the Christian elites of the south and west, that would consolidate between this lineage and assist them in the removal of the Merovingian house. If we assume the Peppinids do not gain some massive propaganda victory over the expansionist and overextended Umayyad at Tours, the Mayors of the Palace are instead known for overseeing losses in the Elbe River Valley which saw the expansion of Slavic tribes against the vassals of the Franks in the Thuringian, Saxon and Bavarian lords.
This is not really true. There are different forms of power in governance and diplomacy and the Peppinids only possessed military might and none else. In a Frankish society that believed strongly in magic, caste, customs and in the potentially of curses, the Merovingians were ascendant. Despite the obfuscations of Einhard and his compatriot Hildwin, the picture that can be gleaned by taking a more critical understanding of the situation, was that the Merovingians were in essence deified kings who focused upon ritualism and matters of military affairs that required their appearance. Their position as a figurehead though was more akin to ideologies deriving from the Iron Age of China, namely the notion of a deified do-nothing monarch who through simply his aura, controls his subjects into correct action. This goes in accordance with the Merovingian foundation mythos given by Gregory of Tours and repeated by others, that the Merovingians were derived from a divine bull and as such, were children of gods, with special powers over other humans exemplified by their ritualized long flowing hair and their preeminent position as sacred entities in the Frankish realm.
When Pepin III requested the advice of Pope Zachary, he seems genuinely disturbed and horrified at the idea of deposing Childeric/Hilderic III and only with affirmation of the Pope, is willing to depose the Great King of all the Franks. This is important in that the mystical implication of curses alone, was enough to hold Pepin III in place.
My argument, is that without Zachary and his predecessors having experienced the implosion of relations between Byzantium and the Holy See, there would have been no Pope who was willing or cared enough to rule on this matter. The Papacy would not be seeking to discover patrons north of the Alps nor would they need such, as the full breach in Byzanto-Papal relations began largely due to and caused by the Arab expansion. Without Papal certainty and confidence in their decision to support the Mayors of the Palace (which they refused to do until the battle of Tours and the end of cordial relations with Constantinople), there would be no words of support from Pope Zachary and thus Pepin III would succumb to his fear and like his predecessors, of which there were 34 prior to him, would be outmaneuvered by the Merovingians in court.
In a counter account to the Einhard depiction, Gregory VII even completely removes Pepin III from the equation of the deposition of Hilderic III. Gregory VII said that, Pope Zachary deposed Hilderic III for not being fit for the position of Christian king. The meaning we can be sure, that the Christian king was one who perpetuated Christianity in their realm as Pepin III and Charles I did, which the Merovingians never did. While it should be taken with a grain of salt, Gregory VII and the accounts of clergy in the High Middle Ages display that a counter narrative to Einhard's romantic interpretation existed, where the coup of Hilderic III was more of a collaboration between the clerical Christian elites and the Mayors of the Palace who only consolidated their power after Tours and after their strengthening of Church ties.
The Saxons were technically still vassals or tributaries of the Merovingians, hence the Merovingians attempting to protect them against easterly pushing Slavic tribes and other folk. The Frisians were likely also tributaries of the Merovingians and there seems to have not been extreme animosity between any of these groups until Pepin III, evident by the Merovingian dynasts having no problem regularly intermarrying with pagan Frisians, Saxons, Angles, etc... Also, I did not only mean them, according to Christian sources, up until the rise of Charles I and his predecessor Pepin III, a substantial part of the Frankish population in the Rhineland and Eastern France remained Pagan and worshippers of various things ascribed them, usually Mercury or something of this nature. Considering the ritual practices of the Merovingians mentioned by Einhard and Gregory of Tours, this is only strengthened in that the Merovingians were enacting ceremonies in mimicry of pre-Christian Frankish deities, especially the deity for whom Tacitus calls Nerthus, supposedly worshipped by peoples inhabiting the area that the Franks resided in. It is also telling that of all of the major Germanic royal lineages, the Merovingians were the only ones to not humanize a prior claimed divine lineage, but to maintain and assert into the Christian era, lineage through divine forebears in the form of the 'divine bull' mentioned earlier.
There simply was not as great an interest in this sort of activity from what I understand. The Merovingians frequently were marrying into Pagan houses, sending daughters and sons about as suitors for pagans whilst also claiming to be protectors of the saints and holy relics, etc etc etc... My view is that the Merovingian house was not so stringent as they are made to be in their religion and had a more pluralistic mentality as far as religion were concerned. This was part of the reason the newer clergy of the 8th century came to despise them and seek to remediate the situation in the country, primarily emboldened from the decline of Byzantine power and the rising sense of Papal initiative built from the Arab expansion shocking Christendom into new and more militant stately forms.
The reason that I bring Bernard of Clairvaux up is that his lineage and formula of society is what did and would impose Christianity upon the populations to the east, namely through bloody conquest and a more thorough molding of the militaristic instincts of the Franks with that of Christian necessity to reform the world, engendered by the Reform Papacy. Much of this was not as enmeshed until after the rise of Islam and the Arab expansion. Christianity would continue to spread, but the forms and styles it would take would be far, far different and perhaps polytheistic in this atl imo.
