Meh.
3-5-2 or 3-4-3 is a legit formation. But I always use 3dc (narrow) never felt like that I lost because my team has only 3 Def players.
Or use 5-3-2 and tag/mark dl and dr with red arrow
But in my experience you won't have any luck with a new formation immediately. You have to let your team play a few matches until they get good and better. I always lost my first matches after i drastically changed formations.
No matter which.
From 4-3-3 to 4-4-2 or 3-4-3 to 5-3-2 I always lost hard the first matches
Plus, I never place wrong positions. Always use correct ones (mc on mc/ mr on mr etc) . Bear that in mind.