To me there are tonnes of variables that are going to help you win a match/league/cup. If for example your team's morale is all set at okay, and you're away from home, I dont think it really matters if you are on paper better than the home side, if their morale is stronger than yours you've a good chance of getting beat.
Then fitness and conditioning comes into play. Then there is team dynamic, which players like playing together? Which players think you are a good coach? Have you got your best actual 11 on the field in the best possible formation? Are they gelled, i.e. have they been playing consistently in their favoured position? Are you choosing the player roles with the thumbs up? Have you even set your tactics?
Pick Porto, play a 442 attacking, manage the team okay and you will get success. I have 30+ goals from both Jackson Martinez and Vincent Aboubakar and it's still January in my game. Saying that, I even crashed out of Champions league. The game is difficult to play. Everything has to be 100% close to perfection as possible to gain success.
I agree the game is difficult, but it's supposed to be. You have to pay attention to all the details, inc. training, finances, board confidence. It's about the whole lot. Being consistent with a tactic is also important. Though I do believe in rotation. Not for the sake of it, but you can rotate players, bring others in and still maintain a winning run. Good luck.