Game : Ayrton Senna's Super Monaco GP II (J)
1st screenshot without fix, 2nd screenshot with fix
c'mon, this is an ugly hack.
The LCD persistence isn't a feature of the video chip, and shouldn't be emulated in the driver, it's misleading and wrong. It's a feature of the output screen device and should be emulated as an option in the core like the scanlines etc. If you hooked a gamegear up to a normal monitor somehow you wouldn't see it.
There are plenty of arcade games which flicker graphics to display them as transparent / half-bright (neogeo life-bars come to mind) but it's not up to the driver to simulate that behavior just because the flicker is more obvious on a PC monitor.