The slide is misleading. From the actual review:
Still, the overall nature of the initial 15-hour-long campaign is fast and fun with no mediocre extra mechanic modes mixed in. Every mission is a monster hunt, and they’re damned fun. Once you roll credits you’ll have finished roughly 1/3rd of the overall game, with the latter parts focused more on leveling your Hunter Rank to progress.
It was a massively disappointing progression curve. By the time I rolled credits the first time I was dumbfounded, as it took me nearly 40 hours to do so in MH Worlds. When I saw how much more content there was after I was optimistic, only to never once feel any of that classic Monster Hunter gear-grind satisfaction.
He's referring to how-long-to-credits.
The "story" in Wilds concludes at the end of LR, which apparently took him 15 hours, whereas you don't hit your first credits sequence in World until you beat Xenojiva, at the end of HR. Furthermore, World had a lot more padding in it requiring you to collect uNuSuAl TrAcKs for hours until you could fight the damn related monsters. To make this a 1:1 comparison is unfair.