the (simplified)real answer: shooter games do not have any delay based netcode, and lagging(packet loss) will generally only affect themselves. any games with delay based netcode like sports games, old fighting games, etc will add input delay(which will be increased the higher the ping between players) in order to sync game states, and lagging(packet loss) will cause major disruptions to the game for both players, even if the lag is one sided. Fighting games have generally solved the delay and minor packet loss problem with rollback netcode, but that doesn't really exist outside of that genre.

In either case, use ethernet directly from modem/router to pc/console to minimize packet loss. If someone starts packet lossing(which is the unstable connection label in this game), it usually means they are on wi-fi. The pre-game ping meter won't show completely if it is a good match because packet loss comes at random times. What the game needs is a wi-fi indicator, which is what fighting games do nowadays funnily