Does Windows really evaluate this flag for the parent executable, only?
Yes.
Is this completely ignored for all DLL modules?
Yes.
So why should I enable the LAA linker flag for the DLL if no one is evaluating it?
You should not. It's pointless.
I had the following: Is there a way to get Windows to issue a warning if LAA allows exe to load a module that is not compiled as LAA?
No. No.
, - . . LAA, . , . PE , DLL EXE. EXE.