I can't check as my PC is dead, but there's no good reason for Valve to use web installers, and in my years of poking around I never saw a web installer for a redist in any of the few hundred games I installed. 'dxwebsetup.exe' vs 'directx_MonYear_redist.exe'. The installers themselves seem to use whatever names they were given by Microsoft or whomever develops & licenses them to others, so if it's a web-based installer it should be obvious (if you can find it in the Steam folder).
The devs can apparently still manage their own installscript.vdf to do this, but it'd be much easier to just opt-in to SCR.
With 'SteamWorks Common Redistributables' (SCR) they are setup by devs, but the install scripts and redistributable installers themselves are managed by Valve. This makes it slightly faster & less annoying as it doesn't have to show the installer window or wait for us to click through the installer. The redistributables are quietly/silently installed using commandline switches/flags.
