And the main reason i posted on this forum was to find out what other cards i should include in my sideboard(especially against oath and combo).
I am a big fan of Night of Soul's Betrayal against Oath. It makes it impossible for them to Oath and has general usefulness against the rest of the decks that run creatures. Engineered Plague doesn't do much against WTF and other Fish builds, since one or two creatures will always slip through, so Night is better in general, especially since you should be able to support the double-black with 3cc.
Yawgmoths_Dummy's suggestion to remove the Gifts is a very good one. To really abuse Gifts, you need more ways to get the cards going from your graveyard. Otherwise, you'll be getting 2 cards for 4 mana, which is not very good, especially since you'll always get the two worst cards. Cutting all 3 Gifts and the Power Artifact, which you really don't need (you can possibly keep the Monolith, if you need the acceleration, but I'd recommend Mana Crypt) opens the way for 2 Scrying + 2 Tops. That draw base is definitely the way to go with 3cC (or 4cC, for that matter). You will always be less explosive than your opponents, so try to make up for that with consistency. Card advantage is your only way to win.
I dislike the Scepter and would much rather have a second Disenchant, since with Tops you become more vulnerable to Null Rod and only have the single out. That's not really good. As for the sideboard, I still favor Exalted Angel over everything else, since you can go aggro versus aggro, and not all but quite a few Fish decks still have trouble with the Angel.
The general question, "why play X-cc Control", is quite hard to answer. Somehow, with all the creatures and artifacts running around nowadays, a removal-heavy control deck should be feasible. The main weaknesses are the vulnerability to Wasteland and the lack of a combo finish. The deck is just too slow, because today's disruption is so fast (Chalice, Workshop). In order to perform properly, I believe 3/4cC needs 5 Strips and the card advantage suite of 4 Brainstorm, 3 Scrying, 1-2 Top in addition to Ancestral and Fact or Fiction, and it will still be outmatched by Control Slaver, Tog and Gifts.
Dozer