but the process of feudalization began much earlier
Feudality being understood as the mix of
benefit (concession of royal or fisc's wealth) usually landed, and vassality (understood as a personal clientelism): or at least with the classical definition used since Ganshof, we're forced to see that it's not existing during Merovingian period.
It's not achieved with Carolingians, it only really appears there at the point both became undistiguishable from each other with the Xth century (before, even in the rare case it was a thing, it was always distinguished).
There was already strong signs in the late sixth and early seventh centuries, with the "civil" war between Brunehilde and Fredegonde
Which is more a counter-exemple, as we're on a fight over the royal fiscus and an unification trend (that would know its apogee with Dagobert, without a noticable dedication of the fisc), not about its dismembrement (even if Merovingian aristocracy managed to get a certain autonomy with regencies and conflicts, but that's more true with the situation after 640's)
As for the contemporary Gondovald's revolt, we're in the continuity of Late Antiquity co-kingships and usurpations, not a political desintegration as it would happen in the late IXth/Xth century.
and the development of the mayors of the Palace who built very powerful territorial power bases
Yes, but that's essentially concerning Carolingians, and Capetians (that weren't majordomo) ducal title didn't really provided them with a completly depleted royal fisc (Late Carolingians basically held only Laon) and they didn't benefited from the guardianship of ecclesiastical demesnes as Carolingians did to establish systematical vassality on landed families.
If something, the coronation of Hugues is related to the Robertian decline, and the disappearance of the huge Robertian sphere of influence in Francia after Hugues the Great's death. Not about its capacity to distribute land.
Peppinids/Arnulfians/Carolingians were powerful, but less about privatized political power on Austrasia (if it was that, their power wouldn't have survived the backleash after Grimoald's demise) but about a huge net of private fidelities on which they managed to get the lead on, without depleting their familial lands along the Rhine.
It's hard to give a year to date the process, but let's say the secularisation of ecclesiastical demesnes by Peppin II and Charles Martel could be the first start, with the councils of 743/744, that allowed Carolingians to do so legally (si necessitas cogat, technically, but in fact as much they saw fit).
Ganshof said:
At the beggining of the VIIIth century, concession of beneficii to vassals seems to have been accidental, never coming from state institutions. When in 768, Charlemagne takes power, the situation entierly changed. King gives largely, as much as lords (dukes, counts, great landowners or potentes, bishops, abbots) beneficii to a large number of his vassals. Without being necessary, the de facto union between benefice and vassality became a regular practice
For what matter Merovingians themselves, and that up to the end, we're in the continuation of Late imperial social structures, mixed with direct fidelities as the
truste.
It's a bit different in other regions, but that's essentially the same in, say, Gothic Hispania (in spite of the, much outdated, protofeudal theory), where a family can have a "favoured" sphere of influence, but where political power and familial patrimony aren't mixed, safe rarily and incidentally.
Which is a long way to get back to the discussion at hand, I agree, but essentially : the political collapse of WRE isn't directly tied up with Carolingian feudality (and its ulterior mutations), even in a long-time context; but to the consequences of an aristocratic takeover and the necessity to replace fidelities and former dynasty's
truste, and thanks to an alliance with Church that allowed Carolingians to use ecclesiastical and monastic demenses to create a new vassalic "class".