Rather self-explanatory. Temporary ghosting added in FH4 reduced ramming in corners, be it due to lack of skill or due to malice, quite considerably, but coop races did not recieve such upgrade. Because Coop and SP do not feature slowdown penalty for hitting wall, many unexperienced players who only do MP for Festival Playlist , end up disturbing races by bombing corners and crashing teammates into walls.
Adding launch ghosting and high speed collision detection from Horizon Open would prevent most cases of corner bombing, by making careless player fly through properly braking teammates and suffer consequences on his own, without smashing into wall, out of road, or PIT maneuver, anyone else.
vs AI it’s not really needed, since AI driving is very predictible and they can detect cars in front of them decently well.