Do you know that Egyptian pyramids were built by the workforce primarily made up of farmers "recruited" from all Egypt, not slaves?...
And if we assume that they actually raised slaves, how they can be considered skilled if they, as you yourself say, weren't competitive? Nevertheless, we should take into account the level of industrial development of Ancient Egypt (or lack thereof) versus Europe after the 14th century (e.g. manufactories appearing in the early 18th century)...
Basically, you can't compare these skills
Slightly higher ranking slaves who call themselves something other than slaves are still slaves.
What you are really saying in your comparison of industrialized Europe versus ancient Egypt is that slavery is not compatible with our current level of technological progress. This is true. Slavery reduces freedom of choice and thus destroys knowledge. It must be eliminated if we wish to progress
You seem to be missing the whole point of what slavery actually is
In short, slaves are waste material, it makes no sense economically to raise them with no guaranteed result. After all, how do you know that exactly this child slave would be a good engineer or mathematician? At max and en masse, you can only expect them to effectively fulfill only simple tasks. Basically, you would be wasting resources raising and teaching slaves if you aim at something more than that. If you want skilled labor, your best option is hire, just like pharaohs did in the same Egypt when they built their pyramids (and here you are obviously trying to get away by excessive extension of the concept). Slaves are captured as human trophies and quickly disposed of. Indeed, if you happen to enslave someone highly skillful, it would make sense to provide him decent existence and enjoy free labor. But you would likely get better results if you just freed that slave and then hired him as a free man
The problem with slavery is that you can capture a highly skilled slave (though this alone assumes that you are invading a highly developed country) and he will likely work for you but you can't raise skilled slaves. Invasion is not an option when you need millions of skilled hands, and still more so if you are an industrialized nation. What's the use of a slave who can't even read, for the most part?
i guess that depends just on how much the masters are willing to invest into the slaves. (e.g. humankind are slaves of the bankers etc. pp.)
I would prefer to stay with the narrow definition of slavery as
chattel slavery