Yeah I mainly look at players game ratings and at my team overall stats (especially
this tab on the Team Home screen, I think it does a great job to quickly see if your team is doing good compared to the others).
In order to understand if the flow of my tactics is good I applied a lot of tips from
this thread
There is a lot to cover but it does a great job to explain what kind of forecheck morphs into a coherent neutral zone defense, etc. I always have this old thread open when I'm playing haha, but I can definitely say that my teams are doing a lot better since I dived into it. It's a great read I definitely recommend to try some of the advices that are given there !
I also tweak a lot of player individual tactic sliders to put emphasis on their role, strengths and weaknesses. For example if I have a stay at home defenseman that is great at blocking shot, I tweak his individual tactic sliders to make him defend more, backcheck more, apply less pressure, play slowly with puck, etc. You'll also find a lot of great explanations about that in this thread.
So yeah I avoid "terrible fit" players for my tactics, but by following this thread I found that a lot of "bad fit" players can still make an impact if the overall system stays coherent. And I'm judging the success of tactic by looking at players game ratings, team stats and obviously if we're winning a lot haha.