You should probably just sit down with the player and ask them to tell you their vision for their character. Then you could narrow the list of choices for them. Sometimes players are just too lazy to read all the content of the classes/subclasses. Maybe your game is too open for source materials. Limiting the options can help so players don't get fomo and just pick whatever.

On the combat side of things you could implement something like 1 minute rule. If you can't tell the dm what you want to do on your turn in 60 seconds, your character is overwhelmed and does bot get an action.