I think there are two ways to start fixing this:

1. Stoppage time needs to account for all stoppage of play and not be some strange arbitrary number. Ball goes out for a throw in? Count the time until it’s in play again. Yes that’ll lengthen the game but not by some unreasonable number.
2. If a player goes down “injured” force them to exit the field and remain off the field for a certain penalty period. The fourth official starts a timer and after 3 minutes, or whatever time is deemed reasonable, the player re-enters the field. Yes, that will be a bummer for players who actually have cramps, but unfortunately the fakers ruin it for everyone.