I'm as guilty of that as anyone - I don't have any grasp of the technical notion of modularity.
All I know is that scaling rates of healing up and down, in a context in which the passage of time within the gameworld is not itself any sort of resource drain, (i) seems not very profound, and (ii) seems merely a change in colour.
Oh, I agree with your main point. I was piling on for one of the reasons why I don't think your point is even seen to be an issue, much less addressed.
After I posted, I realized the part that really chafes is the thought that somehow changing the rate or amount of healing is a useful dial. It's pretty much not, your reason being a prime piece of evidence, but not the technical reason.
Consider for a moment a "better" replacement for the stated rule. (It's better in that it illustrates technical modularity--not necessarily good as a raw rule. But then I came up with it over 10 minutes of idle musing. Also, I'm constrained by the necessary reverse engineering here.)
Let's say that for whatever reason, it was decided in the standard rules that healing works as follows: Every character gets to roll their hit die a number of times equal to their level, and they get to do this up to four times per day. Perhaps the default is every six hours--or after each of the three major meals plus once after six hours of rest. The roll is how many hit points you get back.
Now whatever it's other demerits, there are more dials, levers, and swappable points to play with there. Right in the base is proportional healing by level and class, but not as intrusive as tracking by the hour. You've got the same options to modify amounts and timing, but also easier ways to work in Con mods, modifiers (such as for bad or good conditions), magical aid, etc.
Personally, I think it is too much healing for a default, but that's a question of scaling. And the proposed 1 hit point per level per hour is a straight subset of that rule. All you have to do is decide that everyone gets a d6 for simplicity instead of their hit die, you give them max rolls to compensate for missing Con mods and bigger dice, and then parse those 24 points per level out by the hour.
So 1 hit point per level per hour is not in any way a "modular" rule. It's a particular niche
setting on a more complex modular rule that might get used for simplicity--or in other words, as a way of effectively
factoring the modularity out of the simple system.
Nearly always, when confronted with such, and wanting to change it, is is better to go back to the more rich original system and change it. Then once you change it, simplify to your own tastes.
A "basic" game of particular settings selected with care might be a really bang-up game. A "basic" game of a bunch of ill-considered and weakly designed rounded-off compromises is unlikely to offer much.