Injury is still possible as a trade off to GS/training minutes.
There's no trade off here. Your opponent doesn't show up, there's no game. There should be no chance of injury. You're saying there's a trade off because that's how the game is. You get GS/training minutes because there's no alternative. It would punish the victim. The same way an injury does. Should be fixed. What you are saying, and have said before in previous conversations is nonsense.
If there's no game, then nobody plays, and therefore no minutes are gained for training or gameshape purposes. I don't think that's a preferable alternative by any stretch. One could alternately just give a bunch of crappy players in the form of lucky fans to the team that didn't field anyone so a lineup could be fielded, but that would be rewarding the bad behavior by turning a zero percent chance of winning into a non-zero one, without risk to that team's own players. A random lineup of the players who exist on the roster could be forced, but again this would be harsh to the team who actually submitted a lineup, and doubly so a team has multiple walkovers and different lineups get selected against different teams.
The current methodology is imperfect as well (and I might well go with the five lucky fans as long as I could ensure they had minimum levels of agression), but it's the closest to the status quo: You made the effort to submit a lineup, therefore your players will receive minutes with the risk of injury. Ideally, the scenario should be as close as possible to what happens if your opponent does submit a lineup, except of course my preference is that a team that doesn't submit a lineup should be guaranteed to lose the game with a forfeit penalty, plus lose other economic /training benefits from the game.