Size is all but vestigial in CoC. You derive stats from it, but it's all but useless on its own. The size categories of D&D and the specific height and weight numbers work just as well without needing to be codified in a stat.
I hold the opposite. The size categories of D&D are rather crappy way to model size.
Imagine a size-athletics based game (replacing strength-constitution). And maybe we replace Dexterity with Agility, just to rename everything.
You could have a game where your core basic combat stats are:
To Hit: +Agility+Athletics
Damage: +Athletics+Size
HP: +Size
Defence: +Agility-Size
For a human-shaped medium build (for height), your Size is your height in feet times 2.
So a 5'6" person has a Size of 11. A 6'6" person has a Size of 13. A 4' person has a Size of 8.
A Halfling now has a Size of 6.
We now look at a 30' tall giant; they have a Size of 60.
That sure would make an encounter with a giant something interesting; their bonus damage on hits is +50 even with average athletics.
If that is too much, we rework Size to be a bit exponential. Each point of size is 9%, say, and 10 is 60 inches (5' even, or 150 cm)
Then someone 7' tall (210 cm) is size 14, and someone 3' tall is size 6.
Under this system, someone 30' tall is size 30ish. So +10 to damage, HP per HD, and -10 to Defence. That seems reasonable for a giant.
With this numerical size value, you could even make flanking interact with size mechanics.
And as we go from "S, M, L" to a relatively continuous value we stop running into the effect of the discontinuities at T/S and M/L. Size is just another stat. A PC with size of 20 is 11' 10" if human-shaped. If horse shaped, they are probably a centaur. The mechanics just work; they are easy to hit, have a lot of HP, and hit really hard.