What specifically bothers you about it? Im not sure I understand your objection.
The components to a ritual spell do one of a couple things -- they give a target, they give shape to the intent and they provide power. They symbolically create the connections and form the spell. We don't have any examples where the preparation for a big spell is, 'Cast smaller versions of that same spell.'
Looking for examples from the books, Would it count when Harry went "full ritual" the first time he used Little Chicago?
He didn't use spells to build up there -- he meditated, he washed, he got naked, he lit incense, but he didn't cast spells. And most of that was just to buff his control roll to make sure the casting was safe for him, personally.
Or, I always imagined that the Bloodline curse in changes was a similarly multi-part Ritual, with then doing one stage each time they sacrificed a "Fuel" person, and then a different ritual requirement to actually fire the thing off.
That's not how it's described, though. It's one single, gigantic spell -- a fairly simple one, really. The sacrifices were about putting power into it to extend its range and penetration.
The Genus Locii bonding required like 5 spells, one to call him and 4 elemental attacks to make it stick.
The spells he cast there were
during the larger casting -- they weren't things done in preparation beforehand. That wasn't, "Okay, i cast an Earth spell, that adds 2 shifts to get me to 15 complexity..." it was more like, "Okay, I do my first roll to control 3 shifts of the 15-shift spell... I'll describe that as calling up earth... second roll, another 3 shifts, let's say it's a fire..."
The entropy curse was arguable broken into three different parts, maybe that would be a reasonable restriction to stacking multiple effects into a larger ritual?
Nah, the Entropy curse was one spell, just with three people helping to control it. Kind of like the scene in Shaun of the Dead where they're all trying to fire the rifle together -- one person pulling the trigger, another person helping reload, a third person keeping an eye out for targets, etc. No one person involved had all the necessary skill to cast it on his or her own, so they divided up components of it to help them handle it -- but they weren't each casting spells for it.
In fact, I would argue that it would be wiser
not to cast spells as part of preparation, because spells are dangerous and taxing in themselves. When you're doing a big ritual, you want to do it as fresh as you can -- not after you've spent a bunch of time using up your magic to create the spell in the first place.
It's also dangerous precedent for a GM -- any wizard could, effectively, cast an infinite number of small rituals effectively for free and ratchet up the power of any spell far too easily. If you're allowed to build up a complexity for a big spell with a bunch of little spells, what's to stop this:
Player: Okay, I want to do a 36-shift ritual to kill the badguy.
GM: Okay, you've got a Lore of 4, so you'll have to do a bunch of quests and gather a lot of items to --
Player: Nah, I'll just do a bunch of 2-shift rituals. I can make those rolls easily and it won't cause any stress to call up that little power.