Let me throw all of you a curve.

You are not really comparing apples to apples

Most old heavy boats have low aspect ratio rigs (short masts) and most new light boats have high aspect ratio rigs.

One aspect of stability is resistance to perturbations. You can do some very complex analysis or come up with a simple measure. A good measure is base divided by height.

Imagine a floor lamp. If it is short with a big base and your 8 year old son hits it, it is probably ok. If it is really tall with a small base, the same impact will push it over.

With boats the 8 year old, is wind gusts and puffs on the sails. Being pushed over is stuffing the bow or in the extreme, a pitchpole.

A quick dumb way is to compare length/mast height

If you get a little smarter, throw in the weight of the lamp base - boat length*boat weight/mast height. Because the buoyancy is proportional to the weight, this kinda takes care of the buoyancy near the bow. Really it is probably something like reserve buoyancy integrated over length , but that is way beyond this.

It is not really the length, the beam plays a part so lets use the diagonal ( square root of the length squared plus the width squared)

Also it is not really the mast height, it is the CF height. For a really triangular sail; like a H14, it is 1/3 the mast height and for a really straight roach A-class sail it will be close to 1/2 the mast height.

Take a stab at calculating Boat Diagonal*boat weight/CF length. bigger number imply better stability.

Keep in mind, this does not tell you how slow the boat is or how it behaves when it hits a limit. For example a barge is really stable but it would suck on a race course. The real key is balance and that is something to talk to the designer about