No, -10 points if you win? It's not worth it. I troll the DTs at times (sorry ) with a 5/3 split in order to complete missions with the lesser split containing Caelus Cr, Chiara & Redra; and believe me when I say a draw gives me more points than a win.
Group C penalty is the max you should opt for (just for Zatman imho)
If you're playing just for fun and not aiming for top 150, go ahead and use a Leader if its helping you win.
I can say from experience that Leaders can get you into top 1/3 if you're just looking for the credit.
Obviously you won't get a much better rank than top 1/3 though.
Using a card with a penalty will probably stop you from winning a DT but it can help if your just aiming for the free credit.