@BuZz Yes. I have not tested it personally, but users are reporting it working with composite video.
Note that the timings programming is enabled only after configuring AdvanceMAME with the advcfg utility to add the proper monitor clock information. At that point AdvanceMAME starts generating video mode at runtime, taking into account the monitor capabilities. More precisely, it's enabled if the "device_video_clock" option is present.
If no configuration step is done, AdvanceMAME uses the current video timings, and ask the Framebuffer to do the scaling, like in your changes.
Likely the only difference is that it takes into account of the aspect ratio.