Don't ever compare weightlifting to MMA. MMA is like powerlifting. They are underground sports that will never make it to the Olympics.
It is undeniable that a former Olympic Weightlifter who at least maintains his level of power and strength will have a much MUCH more powerful roundhouse kick than a "Muay Thai/K-1/UFC champion" who's been training for decades (granted of course, the Olympic Weightlifter at least is capable of delivering a roundhouse kick with optimal technique with full speed).
Like I said, do not ever dare compare MMA to weightlifting. I get offended when people compare inferior sports to a real sport.
You do realise that optimal technique actually involves turning your hips?