Giant weaves their own CF from threads and formulates their own resin. They make frames for many other companies at many price points. Their own design team does outstanding, innovative work. Their crash replacement warranty is second to none. I can speak from experience that they stand behind their product.
Yes they are the worlds largest bicycle manufacturer. Merida is second. Merida owns 49% of Specialized yet Giant builds Specialized CF frames: //www.declinemagazine.com/bike-brands/where-are-specialized-bikes-made/
Making Giant CF frames: