Forged means the molecular structure has been compressed.
The forging process can create parts that are stronger than those manufactured by any other metalworking process.
If Glock & other polymer framed handguns can get away with a plastic frame with minimal metal support, it seems a cast frame would be more than strong enough to suffice. I know some frames wear or break, but I've not experienced any, in the 45 yrs I've owned, in a variety of brands & calibers.