Joshua,
Wow, this one has me stumped. You've made a couple key observations already: that the answer hinges on whether that hc limit is grouped just with the previous sentence or the entire paragraph above, and that this ambiguity is the result of changes from the 2016 standard. In isolation, I agree with your interpretation of this language, but this does not strike me as being the intent of the change, which explicitly addresses drift width w and only incidentally separates hc from other language shared between windward and leeward drifts (more on this below). To me, the hc limit makes sense regardless of the direction of wind: when the snow drift smoothes out a step between horizontal roof surfaces, there is no longer aerodynamic shade to accumulate further drifting snow.
I always found this section confusing because hd is an appropriately named symbol with physical meaning for leeward drift, but a purely theoretical intermediate step for windward drift. Prior to 7-22, the "Drifts on Lower Roofs" section was essentially unchanged dating back at least as far as 7-02, the earliest version I've ever looked at in any depth. I suspect that this method for leeward drift dates to the original ASCE 7-88, and that the 3/4 hd for windward drift was added after, although I haven't been able to dig up 7-88 so I can't be certain. The commentary in 7-22 suggests that they considered revising the 3/4 ratio along with other sea changes to hd including the new winter wind parameter. The committee decided that 3/4 was still close enough.
It appears to me that two changes have been made to this section in 7-22. The first is to separate the windward and leeward methods for determining drift width by appending "for leeward drifts" to two existing sentences, and adding "For windward drifts, the drift width shall be taken as eight times the windward drift height or 8*0.75*hd = 6hd." The second is to add a line break to this admittedly dense paragraph, which in this case has created misleading implications around hc. The code revisions approach tends to be minimally invasive changes targeted at specific provisions, and preserving the greatest applicable amount of existing text. In this case, it may be time to more comprehensively rewrite the section for better clarity. I would suggest submitting this issue to the 7-28 committee.
https://www.asce.org/publications-and-news/asce-7#:~:text=Call%20for%20public%20proposals%20for,for%20the%202028%20revision%20cycle
https://www.asce.org/communities/institutes-and-technical-groups/structural-engineering-institute/committees/sei-board-of-governors/sei-technical-community-executive-committee/asce-7-28-minimum-design-loads-and-associated-criteria-for-b/asce-7-28-snow---rain-subcommittee