Wine aged in oak barrels will be polluted by the unique flavor substances of oak. Specifically, French oak can give fragrance to spices, herbs and toast, while American oak can give sweet taste to coconut, roasted hazelnut and leather.
Oak can give wine enough tannins, but: first, oak will not produce elegant and delicate aromatic substances such as vanillin after baking like oak. Second, the permeability of oak is too strong, and the aroma of wine comes into contact with oxygen in the air, which is oxidized and loses its flavor.
So oak is certainly not as good as oak barrels.
Finally, oak barrels are very expensive. A brand-new French oak barrel, 700 euros each, usually only lasts for 2 years, which is almost 600 bottles of wine. Therefore, if the wine is brewed in French barrels, then each bottle of wine will cost 1.5 euros. The price of American barrels is one third of that of French barrels, but I'm afraid domestic oak barrels don't even need this tenth price.
As for the extent to which the Great Wall uses oak barrels ... Stop it.