hi, I am not sure I know the answer but as nobody else gives you answer... I will try.
First assess your strikers. Are they big and strong or are they fast and not very strong.
If they are really strong guys they should be able to hold off the defenders. In this case try to stick them in the penalty area and to deliver crosses or passes to feet so that they can score. try this by setting them with normal FWR and relatively low creative freedom. Then set your team to play wider and to pass to the wings. And set the wingers to cross ofter of course.
If your strikers are small and fast (like saviola)then you can benefit from playing fast tempo higher creative freedom and shorter passing to benefit from their skills (like barcelona does). the strikers should have high CF, FWR, and probably run with ball.
If you have a big-small combo, then try to vary your tactics according to what the defense offers you...
About the 4-2-3-1: I do not know the Millies tactics so I do not know what may be needed to be changed. But my logic is this: take a look how you concede goals and make changes accordingly. If you often get tormented by the opponent AMCs, then probably your tactics does not guard them well.
Try to find the logic of the tactic! Who is supposed to guard them? One two or more players? Do they have the skills needed to do the job? When you answer these questions solutions will present themselves I think. E.g. if your DMC is slow and weak you may need to buy a better guy as DMCs need to be physical. In the mean while you may need to reduce his mentality and closing down so that he stays in the way of the AMC (and probably hard tackling to injure him

)
hope there is some use in this