In my experience (~5 years of Shin Kyokushin in Tokyo - after ~25 years of other arts), Kyokushin tends to accept whatever you can make work in sparring, and doesn't care too much whether your mawashi geri has a healthy dose of maegeri in there, even in gradings. But individual instructors and examiners may vary.
Of the kicks in the video you link, several are impressive in their minimalism and effectiveness, but the kick at 1:59 stands out as a great example of what's possible if you have great flexibility: he's rotated the hips over a bit more than most of the kickers, so the top hip is close to the top of its arc and moving closer to horizontally at impact. If you can do something like that, it's easier to clear the opponent's guard and shoulder, and he's completely messed with the timing of the attempted block. (Kyokushin fighter Glaube Feitosa does something similar in this video - the slow motion at 0:54 is worth watching).
It's something to aspire to. I wouldn't worry about it too much though - just keep stretching and kicking high and relaxed at least a few times a week, and see what happens for you. During pad and bag work, make sure your kicks are making reasonably impact, even if not at the ideal horizontal angle, and let that improve over time. For the low kicks where you don't have to compromise, make sure they're rock solid.
An even fuller rotation - where the toes of the back foot end up pointing backwards before impact and the kicking hip has rotated over and past the supporting leg's hip, with the body linear and top shoulder rotated over - is used in some arts (e.g. short slow demo execution). That's rarely seen in kyokushin, as kyokushin tends to be keeping the body squarer to facilitate recovery into a fighting stance, using the kicking leg to kick again or block a low counter-kick, and follow up with hand techniques. In Kyokushin you will see a looser kick that rolls right over and is fairly often followed by ushiro mawashi geri (or the threat thereof), normally employed at more of a distance when the opponent's already backpedalling so is unlikely to be able to close the gap during the much longer recovery period wherein it's relatively difficult for you to defend.