As far as I know, the hole handicaps are still supposed to be assigned relative to gaps in difficulty for an 18 vs a scratch golfer.
It's not really that way anymore.
https://www.usga.org/content/usga/home-page/handicapping/roh/Content/rules/Appendix%20E%20Stroke%20Index%20Allocation.htmIt is recommended that a stroke index allocation be applied over 18-holes, split into six triads with each hole ranked on its playing difficulty relative to par. The difficulty of each hole can be determined objectively using hole-by-hole data provided from the Course Rating procedure as follows:
Basically, figure out the "relative to par" difficulty of each hole for the scratch and bogey golfers, break them into triads, and follow some basic guidelines from there.
The USGA and R&A found out that, outside of doing something dumb like putting the holes 1-18 or 18-1 in order, matches come out just about how they would any other way, regardless of where the strokes come. In other words, so long as the strokes aren't all front-loaded or back-loaded, matches work out even if you somewhat randomly assign strokes.
The above system is easier to apply as golf courses don't have to send in 400 scorecards and nobody has to manually enter them. And it's "good enough" that matches almost all work out how they would.
So now, relative to par, they almost are more about "difficulty" than what they used to be: where the higher handicap player was more likely to need strokes. Though that will still tend to hold, as bogey golfers stink at par fives, and those relative to par figures will tend to be high.
(Those are also all recommendations. Courses can do whatever they want with stroke allocation.)