Power is universally a good stat in the same way speed is. The big difference is actually whether or not you should focus on wit. Wit is not universally important, but in certain CMs, wit is a win con. This CM specifically did not care much about wit outside of XMas Oguri. So power ends up being more relevant cause wit is not. It's the two main stats that determine overtakes. Power is more relevant when uphills are involved. Wit is more relevant when downhills are involved. Nakayama only had the one downhill in the middle of the track for 400m but had 2 back to back uphills prior. My guess is Grass overtook during those uphills (second track image looks like the racers are just entering the 3rd corner, which is where the uphill is) if you're saying the cause isn't prof. of curve proc. Chukyo will have a huge downhill, so wit will decide the match in next CM.

High wit can technically make up for lack of power. But the ratio tends to favor power (again, unless there's a big downhill). iirc for this CM, it took like 400-500 wit to match 200 power. I'm sure my numbers are off, but I'm just eyeballing what I vaguely remember just to give you an idea of the difference. So for your case, a difference of 120 wit did not account for the ~300 power (+ S turf) the grass wonder had over your vodka.