Mortal Kombat had a huge cultural impact in 90's U.S.A because it was controversial and fresh. Definitely one of the most defining waves of the 90's.However, it never had an impact on the fighting game scene, even in the 90's. I'm not saying it's a bad series, it's one of my favorites, but it was never taken that seriously in the fighting game community. Things started to get better with Mortal Kombat 9 and I'm really looking forward to the newest installment.
Personally, I don't consider Smash Bros. a fighting game for a laundry list of reasons; It's a really fun and well made party game. Everyone is entitled to their own opinion, though, so if you do that's okay too.