I agree with a lot of this but why is there a presumption that Caste System is needed to research Liberalism? I rarely if ever use Caste System at that time. There are so many uses for Slavery, not least of which is spreading the religion needed for Pacifism, I then build the monasteries in science cities for an additional research boost.
The argument for early Pacifism is based upon its ability to speed up the progress toward Liberalism. The higher number of Scientists allowed by Caste System will help speed up the generation of the next Great Scientist. Although I do not think this is a strong enough reason to prefer early Pacifism over late Pacifism, a focused effort of research towards Liberalism can be helped by using Caste System rather than Slavery.
Is Caste System really that useful between CS and Liberalism? There are several ways to get Liberalism and one I've found useful is to research Paper and then use 1 GS to lightbulb part of Education researching the rest normally. Then immediately start building universities in key cities (and enough other cities) such that by the time the capital has built its university I can whip/ build the others needed for Oxford. That allows an early start on Oxford and really sorts out the research problems for a while at least.
The usefulness of Caste System largely depends on timing.
As you point out here, switching out of Slavery too early can stunt the productivity of your cities...this is why I prefer late Caste System. With late Caste System, you will more likely benefit from the +1 hammer bonus for workshops. Regarding Universities, however, I often find that they are too expensive for non-Philosophical leaders, especially when using an early Education tech path. The population spent by whipping them can instead be used to run more specialists during Pacifism. If you also lack Stone, then building Oxford University becomes especially expensive.
I might use a GS to lightbulb Philosphy in which case I might run Pacifism with Slavery, especially if I'm also Philosophical. That gives a double boost to GPPs and means that Slavery is available to whip the cheap universities into weak cities. I'll often run a spy part time alongside the two scientists to further boost the GPP production. Slavery also means that warfare is possible as it recovering from earlier warfare by installing infrastructure. Caste System is particularly unattractive at this time if warfare is likely. Without Guilds or Chemistry it means that workshops are a weak improvement compared with chain irrigated farms that allow big cities and rapid re-growth after a whip.
I find that the Philosophy bulb is the most useful of all the GS bulbs, by far. The Education bulb is often not sufficient to finish the tech on its own, and in many games it's possible to delay Education in favor of more practical techs.
If you commit yourself to one specific GS bulb in your strategy, then you can better control your overall strategy. The only time I would not do a Philosophy bulb would be if I built an early wonder that popped some great person other than a GS. An Education bulb, on the other hand, is unheard of in my strategy. If I wanted to, however, I could substitute an Education bulb for an early Academy, and delay the Academy until the 3rd GS is popped.
Regarding the Slavery + Pacifism combo, I see a drawback. Although this combo gives you a lot of options, these options are counterproductive with each other. Slavery requires surplus food to recover from whipping, and Pacifism also requires surplus food to run many specialists. Being able to do either one requires sacrificing the potential to do the other.
This is why I prefer to do the whipping beforehand, while I'm still in Phase 1, and wait until Phase 2 before cranking up the specialists. As a result, the duration of Phase 1 is extended for this reason. Although this also delays the generation of GSs, the focused application of the 2 GSs I generate during Phase 1 is usually enough help for winning the Liberalism race.
I usually research Liberalism normally often building research or wealth if the race is tight. I don't even know what the conditions are to lightbulb it with a GS

but I might do it that way if it wasn't too difficult. I sometimes use a GS later on to lightbulb part of Chemistry, but that's another story.
The option you mention here of building research or wealth can actually be combined with the late Pacifism strategy to shoot for Liberalism. However, it requires conserving hammers so that you have enough of them to build your skeleton infrastructure. This is why my recent games tend to delay Universities and other expensive buildings.