At the end of the day this game comes to players and how good they perform, we all may have witnessed a team in our servers that keeps winning despite the formation.
I had a really really bad league season (there is an unbeaten team leading and some other competitive teams and that means massive troll results), but in the CL I reached the final, surpassing my wildest expectation. I used same tactics and despite knocking out active higher level teams in CL, I struggled with the good old abandoned teams in the league like always. My players performance was the key, I had 5 or 6 players constantly getting 8 and higher marks. The game determines which player Is gonna be your scorer and all the ones that will have a key impact in your journey beforehand.
A bad player will always be bad and a normal player will always be normal. I experimented with many of mine by giving them SA and new positions out of curiosity and nothing happened.
I change tactics during those games that everything seems to go wrong all the time and 90% of the times in my case nothing happens.
Tactics seem to matter more during the times that my team is being surprised by a lower team.