I’ve experienced many of the same frustrations as you and that is why I don’t spend money on this game. The community has pleaded with EA to make improvements to gameplay and they refuse — instead, they spend their time making changes no one asked for — like substituting this lousy “draft” system that pretty much everyone hates for the shard system that everyone liked. In short, their actions are nakedly self-serving and show no evidence of actually listening to the community.
As for Manager Mode specifically, there is nothing you can do to affect the outcome. A higher OVR helps marginally, but it is not decisive and no amount of tinkering with tactics appears to change the action on the field. Personally, I’m stuck in the first tier of FC Champions and recently went 16 matches without a win. That’s right, you read that correctly — no wins in 16 matches! During that stretch of a few days I made no changes to my tactical approach, but the simulation just randomly handed me poor result after poor result. So, my advice is to set the simulations to run so you can collect the points, but don’t waste your time or energy trying to win because it will only result in frustration.