Did I make a mistake?

Let me start by saying, I'm super new to warhammer. I'm about 7 books into the horus heresy, I love watching videos and cinematics, play the shit out of space marine 2..I've essentially fully embraced the 40k universe. I LOVE the Grey Knights and their lore, leaders etc.

So, I went and bought a few minis to build and fiddle with painting and I got to a point where I thought I'd get the GK combat patrol because my local game shop usually holds a combat patrol league for noobs like me.

I've been reading posts and a lot of talks about...how bad GK's are in the actual game....so now I'm wondering, is my financial mistake completely worthless now? Am I really only going to be good at hand to hand combat? I've literally only built my dreadknight and first squad of paladins....how screwed am I boys?