I agree with that. Bosses like Shao Kahn are more unique because they are not characters which one can select. This makes it funner to fight them. I think bosses like Kintaro and Shao Kahn (MKII) are the coolest bosses in any MK game. The more recent MKs had bosses like Shinnok and Quan Chi (MK4) and Quan Chi and Shang Tsung (MKDA), and in my opinion, were not that fun to fight.

I kinda like how it was in MK1. Goro was big and tough but Shang Tsung was easy. But you couldn't select either of them. Shang Tsung wasn't super big and strong and fast like Shao Kahn was. He was a little tough, but not to the extent of Shao Kahn.

id rather have a unique boss like shao kahn because it gives you more of an achievement feeling when you win or that you even made it to the boss.

Goro and Shanstsung From MK1
Shaokhan From Mk2

Shinnok is joker

Bosses like MK1 Shang Tsung, and Shao Kahn were so much better than Shinnok and the Deadly Alliance. Its stupid when the boss is a normal playable character, it takes away from the feel of a true fighting game. Thats the only thing I like about MKD, is that the Dragon King isn't a normal playable characer.