The number one priority is building a strong strong team. This is then followed by the basics and tactics.
I'd put it like this;
Team strength > basics/tactics > luck
If your team is around the 800+ strength mark, you don't need to worry about advanced tactics to much.
I lost 3 top players around the same time halfway this season, replacements aren't bad players, but still need 2-3 seasons to be elite. Went from challenging for the win in FL1 to barely taking any points.
This showed me the importance of squad strenght, especcially when playing the top teams on this game.
It makes building your team very interesting. You can go for a top squad that peaks for a few seasons and then has a few seasons to rebuild, or try to balance and challenge every year, but not have 11 peaked players.
The fun part for me in this game is that nobody really knows how game results are calculated.
Are certain formations better against other formations?
Does having Shooting 99 on a defender have that much difference than 85-90? (same as tackling for a STR)
What player is best to play. Maxed 99 SKILLS and low gelling/morale or a average player with high morale/gelling
...
In my opinion the result mechanics are in a fine state. So many different variables that you can try to outperform others by that make a difference, but nobody really knows the impact of each.
Losing by luck sometimes is part of the game. You will also sometimes win by luck, so it eventually equals out.