Some movements in karate though can't be done with the same fluidity and motion than lets say, taiji. Why? Because you might be doing movements that require tension, or muscular movement, or the alignment won't allow it. In some schools, the reason seems to be because "intensity" is often shown by actually physically showing it, wether in the eyes, the "kias" or the movements. People in my Xingyi Class who practiced karate earlier, often STOMP real loud, and tense their muscles at impact..to show "power." This , in my own opinion, is wrong. Some even "HUMPH" and ""HUGH" real loud in their breath, leading for physical tension in their body and mind, almost subconsciously.
Main thing to realize is that "intention" should be an internal thing, ,and not an external thing. Your external form becomes a direct manifestion of it..not the other way around. Being tense, yelling real loud, and wasting energy does not mean your intention is stern..Anyways just my 2 cents on the problems with alot of modern-day students, including me sometimes.
Nowdays though, and the past (since karate pretty much originated from old kung fu anyways), karate teachers/masters cross trained with CMA styles. And then they try adding circular non-linear movements. Or do their movements like other styles. Which is why you always see "new styles" with kakie practice, or heavy xingyi influence.