I've also tried to test tactics with "Go On Holiday" thing and I can say that such testing is a complete bullshit
I found that when you "Go On Holiday" then there's no one left to handles your players' personal issues and after few months all your players become "Unhappy"/"Concerned" so their morale takes a serious hit due that.
Also, I found that the assistant manager doesn't properly rotate the team and he makes idiotic choices when it comes picking the team.
At the screenshot below you can see how my team looked after I went "On Holiday" for few months… almost all players were "Concerned" or "Unhappy"... as I said a test with "Go On Holiday" is a bullshit... don't bother with it
Even the worst FM players can get better results with any tactic and any team than the results that you get playing with
"Go On Holiday" thing