Jan, thanks for your great response. You have expressed yourself thoughtfully and quite succintly- I'm the rambly one !
I shall attempt to do justice to your post and ask you
(and Barbara) to overlook my shortcomings,...well, here goes.

We know JA tells us 'Elinor had an excellent heart; her disposition was affectionate, and her feelings were strong: but she knew how to govern them: it was a knowledge ...which one of her sisters had resolved never to be taught.' (ch.1).

My impression is JA intends us to see Elinor as warm natured yet she governs her feelings with sense and intelligence.

I think you perceived my definition of 'sensibility' is simplistic.
Dr Johnson gives two definitions of Sensibility 1. Quickness of sensation. 2. Quickness of perception.

Sensibilty applies to thought as well as feeling; thinking and seeing conducted sharply and quickly.
And I believe you are right- JA's contemporary readers would regard Elinor as possessing as much Sensibility as Marieanne...

Elinor suspects of Colonel Brandon 'the misery of disappointed love had already been known by him' (ch.11) she shows her sensibility- being sensitive and quick in her perception.

I am sure Elinor does not hide her innermost emotions due to society's rules. Rather, she uses her own judgement. I think she accepts her social role- she's polite to John when they meet. Yet she remains aware of the truth of people like Lucy Steele.

In regard to your point re: Elinor's sensibility is actually greater;
Her suffering re: Edward is intense yet passive while Marieanne's is more active. Elinor is less willing to bring the pressure of her own individualism or personal needs to every incident.

Yet Elinor can be attentive to social forms. After Willoughby abruptly leaves, she tells her mother 'I want no proof of their affection but of their engagement I do'. (ch. 15)
Elinor's also excercising her judgement as well. Yet feels very sorry for her sister.

The title tells us 'Sense And Sensibility' can mutally
co-exist. JA's linkage is the 'and' of the title.
Yet to judge by many S&S posts, in my opinion the tendency of JA's writing invites the reader to see contrasts between Elinor and Marieanne.
Perhaps JA was attempting two different things with the novel. To present a point, at times she polarized a theme or charecter, like Sir John. ;)
At other times, JA suggests the two qualities can co-exist in a harmonious tension as she shows within some charecters.
( I use the word 'tension' here re: a sensible man such as Col. Brandon in a duel.)
At this point in the novel, Marieanne needs to excercise judgement-so she can use her Sense to govern her Sensibility.

As for the see-saw notion in the S&S1 credits, I don't know if distorting mirror images of the sisters- their eyes and expressions- would reflect interactions of Sense & Sensiblility within individuals more accurately or maybe too abstract.

Debates on sense and sensiblity or reason and emotion or the Nature of Man- good or bad ? raged in society in various forms through the Eighteenth century, sometimes called the Age of Reason. My impression is these ideas are an unfinished perpetual debate.
I'm unsure how original JA was in her ideas of reason, feelings or human nature. I believe JA's main quarrel with the cult of Sensibility was people are encouraged to exaggerate and falsify feelings and she felt this did not excuse people from observing common decencies of social behaviour.
My impression is with 'S&S', despite it's presentation, JA did not set Sensility as a point diametrically opposed to Sense. Rather to examine the broad spectrum of behaviours both terms can encompass within individuals.

Pardon lengthy response. I hope these thoughts are of some interest and not too rambled. :)