I think that your grudges and rancor against certain companies ("M$") has you interpreting the facts a bit incorrectly. . .
A clean/pristine of Windows 10
does include dx9, 10, 11 DLLs. As well as D3D9on12.DLL.
LotRO doesn't fail to run appropriately on Windows 10 because Windows 10 is lacking DirectX 9 compatibility overall but rather because a couple of very particular DirectX
extensions aren't included by default in Windows 10 (and perhaps every other edition of modern/supported Windows) and LotRO fails to install those
extensions as it should.
As documented
here, all that's needed for Windows 10 to run LotRO fine in DX9, DX10, or DX11 mode are two or three DX
extension files. The recommended way of obtaining which is installing the runtimes.
One suspects that games that don't depend upon such extensions will run fine in DX9 mode on Windows 10. And those which do depend upon them should be installing them appropriately on every edition of Windows (not just Windows 10). But, alas, the LotRO installer fails to do so.
Put another way, it's more a problem with LotRO's installer than with Windows.
--H
P.S. I suppose this post will be seen as "sponsored by M$"