I've read a few articles saying the decks in the Core Set are largely balanced, with perhaps the Targayen deck being a bit weaker.

I was hoping to get more experienced players' thoughts on the deck balance?

I just played my first match (me: Baratheon, opponent: Lannister) and I got creamed; I just couldn't keep up with all the "deadly" characters and their gold generation.

Thanks!

I didn't really think they were balanced. The Stark deck has like 2 intrigue icons in the whole deck, right?

I think they are reasonably balanced for melee, can't remember the last time I played with only core set decks though. I don't remember them being all that balanced for joust though.

I think they're relatively balanced for a 4-player game.
A second copy of the core will go a long way to balancing the Houses for a 2-player game, picking up a third core would be ideal, and switching the plots around (even with just 1 core) would help a bit - one of the biggest problems is the single copy of Valar.
I actually think the Targ deck is pretty good if you have multiple cores, a lot of the Targ core cards are good in any deck (Forever Burning, Flame-Kissed, Lady Daenerys Chambers). The same for Bara (Robert, Stannis), not so much for Stark and Lanni, though there are exceptions (Golden Tooth Mines). Having extra Seas, Fiefdoms, Limit 1 per deck, and +1 Gold locations is really useful too.

I found theyre pretty unbalanced for 1v1 play, which is irritating. I say the quickest way to balance the decks would be to move around the plots and never play against Stark without a Valar in your deck. Could even go as far as saying Condemned by the Realm is blank/counts as a different plot (since its basically useless in 1v1)

If youre set on playing the game and investing in it either another copy of the core set or deluxe expansions are the way to go. Another core would do a lot to make all the begginers decks more balanced and the deluxe expansions are great if you have one house youre set on playing and want to get a huge boost in strength for it!

They aren't balanced in 1v1 at all. The Baratheon deck is a pile, for starters. The plot cards are completely at odds with what the deck is trying to do, and it has many weak cards. Reshuffling the plots would definitely go a long way toward balancing them.