@randomtask The whole purpose of restricting the modern mapping to kof/ffury/samsho (then to vs fighting games) was to avoid having the modern preset changing the layout for games like metal slug. This modern preset was a suggestion from @manulegil to mimic the layout of snk fighting games on modern console from the last decade, having it on every game makes no sense and is kinda harmful since most people prefer using this mapping :
--- ( - ) ---
(C) -- (B)
--- (A) ---
over this mapping :
--- (C) ---
(A) -- ( - )
--- (B) ---
for 2 and 3 buttons games on neogeo.
You can still use the remapping feature from retroarch on a per game basis if you are unhappy with the presets.