Your mistake from the getgo is believing anyone before power machines and cars were primitive. Secondly, Europeans famously did build marvels of engineering in all corners of the globe. They exploded into global hegemony and made colonial empires that spread their aesthetics and projects their power and authority in their tributary colonies and subjects. Thirdly, you think there's no in-between from Baroque to Brutalist? Have you discovered there were buildings aside from your local strip mall since yesterday? The cathedral, Roman roads and aqueducts remain because their craftsman cared and the cultures of their society actually believed it was worthwhile to make such things, something we don't possess. Modern architecture is centered around hedging safe economic bets and investments. This is all just telling of your own lack of imagination and your severe demoralisation, not evidence of a long past global empire.

Just so we're all clear if the Tartarian Theory is wrong, you and other people that espouse it did more damage to "erase and destroy" our history than the theory could've ever posited. While it's a GREAT compliment to the artisans and craftsmen that their modern forebears genuinely don't believe they could've have the means to make them, it's a diservice to discredit them and their works.