D&D has opted to be a mile wide and an inch deep, and it's too late to change that. So we just have to get used to the consequences.
If you wish to use such a jaundiced description, that's your bag.
I see it as choosing to be 44 yards wide, 44 yards long, and 44 yards deep (44.147^3, if you prefer). A cube, the thing which minimizes surface area for a fixed cuboid volume. As opposed to being a foot on either side, and 440 miles tall--perfect to send you soaring to the highest heights if you fit into its single square foot of area, totally useless if you want to go anywhere else.
Which is precisely the problem with what you advocate. Other games can get away with it because they aren't
trying to offer something that most people can get into.
In fact, I have the
perfect analogy here. You're saying everyone should switch to Macintosh computers, or go all the way to Linux--that Windows shouldn't be used by anyone, because casual users benefit from the closed ecosystem of Apple products, and serious users benefit from the almost complete control Linux provides. Except that there
really actually is benefit in Windows offering a middle point, something which has most of the complicated stuff taken care of for you but leaves open the possibility of restructuring it, up to a point. That package genuinely appeals to a variety of people, and is a significant but far from unique/determinative, reason why Windows is the dominant product in the personal computing market, even with it very slowly losing market share over time. (It's still 2/3 of the market.)
Perhaps--
if the TTRPG market had been carefully engineered from the very beginning with a focused plan--such a thing could, potentially, have produced a better result. But at this point, this is like saying that base-12 or metric time would have been easier to work with and better for everyone. Yes, we could
theoretically convert to a base-12 number system and fully metric time...but it would be enormously expensive in time and money both, for pretty small benefits. Same with converting to true metric time and thus changing
every single fundamental constant that in any way relates to amounts of time (generally, because you're changing what "a second" means).
More or less what I'm saying is, the thing you propose could only have occurred if TTRPGs had been precision-designed from the ground up with infinite scalability and scope in mind. They weren't and almost certainly could not have been so. As a result,
whatever system took the crown would have ended up in the position D&D is: having a distinct flavor of its own, but used for a wide variety of experiences.