Not all of those situations are created equally. A bases loaded situation when the game is 10-1 in the 7th inning isn't the same as coming up with the bases empty in the 9th inning of a 1-run game. The sample sizes are also not equal throughout. Factoring for leverage, which is what goes into the Clutch score, here's Harper's career averages:
Low Leverage - 134 wRC+, 2319 PA
Medium Leverage - 145 wRC+, 1737 PA
High Leverage - 130 wRC+, 458 PA
Career: 138 wRC+
Maybe he's uncannily good at coming up in like 3-run games with a runner on base, but this basically says that his hitting profile isn't much different throughout the different scenarios. And if you go and look at the year by year data, which I'm not gonna lay all out, there's also plenty of variance in each context.