I'm a huge stickler for technique and come from a striking background. (I've done boxing, karate, TKD, and Muy Thai) I also gamble very heavily on MMA and dissect the smallest elements of a fighter's mechanics on tape regularly.
Thus, I can confidently state that that Semmy Schilt's technique was good. Was it the very best? No. Were there certain things he couldn't do other heavies could? Sure.
But he was certainly good, even by the standards of world-class kickboxing, then and now, and presented a riddle that no one really solved.
He was a nearly 7' guy with a good jab who, if you closed the distance, would splatter you with either his left hook or his brutal knees in the clinch, some of the greatest in kickboxing history.
For a guy with such a monstrous height and length advantage, that's really all you need. Those aren't my words, either, but the legendary heavyweight boxing champion Larry Holmes when talking about the match-up problems Gerry Cooney presented him, another very tall guy who had a good jab and powerful left hook.
As for "losing" to Hongman Choi, you realize that was a blatant hometown robbery? (The fight was in Seoul)
Nevermind that Choi was an okay kickboxer with a number of good (legitimate) wins before medical problems curtailed his career, dropped a prime Badr Hari, and went to extra rounds against a JLB only slightly past his.