YES!!!
All the "secret" skill and moves don't mean a thing if you don't have the power and the conditioning. Strength is just as important as skill and techniques. I've seen a famous master in TKD, his technique is very good for sure, but he is not strong from looking at him in the gym doing weights. If he has to fight with a strong guy that has not done any training, I won't bet on he can win. If he cannot drop the guy on the first kick or punch, he might be in for a big surprised. If the guy gets hold of him after withstanding the first strike, he might be wrestled down, distant will be too close for any effective strike and there is no way he can out muscle the strong guy.
Fitness, strength and conditioning is every bit as important. That's the reason I do 50:50 in my exercise regiment. 1/2 the time on strength and half divide between kick boxing and stick fight. I am training at home, I am close to 69, part of the weight exercise are 20 pushup wearing 60lbs weight jackets with feet on the chair for 5 sets( less reps on the last two sets), bicep curls of 40lbs dumbbells, squat with 60lbs jackets and 40lbs dumbbell on each hand etc. as my weekly regiment. I treat my kick boxing and stick fight as aerobics, I hate running!!!