Some questions need to be straightened out:

Cross-tuning - "scordatura" - exists in Classical music as well. The seventeenth-century Austrian-Czech composer Heinrich Ignaz von Biber became a specialist in cross tunings. He wrote a set of Biblical violin sonatas corresponding with the different stations of the cross as depicted in the Catholic church. Each one of these fourteen sonatas uses a different cross tuning: one using the standard tuning and thirteen other cross tunings which excell the number used by fiddlers. In addition, scordatura became a popular Austrian and German technique that spread to Western Europe. Before this, the English technique of the lyra-viol employed a number of different tuning systems as found in John Ford's "Diverse Aires" of 1611. Finally, the American, Benjamin Franklin wrote a string quartet while in Paris which is only scored for open strings using four different scordatura by the three violins and violoncello.

Regarding improvisation - Classical violin technique during the sixteenth and seventeenth centuries incorporated many instances of improvisation that are lost in today's technique due to the virtuosic changes in Romantic music of the nineteenth-century. However, the sonatas and concertos of Corelli, Vivaldi, Handel, Geminiani, and Bach incorporated an understood form of improvisation into their compositions. In a sonata, partita, or other type of solo work, a repeated section would receive an improvised variation on the repeat. Ornaments, graces, and bowings were subject to improvisation and remained a fixed performance style into the end of the eighteenth-century. Again the Romantic movement stopped this improvisational style. Nunmerous treatises and documents exists explaining this process - 1.) Christopher Simpson, an English viola da gamba performer published a treatise on how to improvise variations called "divisions". This Classical approach of improvisation soon spread to Scotland where composers such as William McGibbon borrowed this ENglish classical approach and created Scottish fiddling. Other English examples of this practice can be found in a book called "The Division Violin" published by John Playford (the publisher of the "English Dancing Master"). Division style proliferated around lowland Scotland until the Gow family stopped this traditional Scottish style. In essence, Classical playing created Scottish fiddling and other British forms of fiddling. Francesco Geminiani also published a version of a solo sonata by Arcangelo Corelli which presented both Corelli's printed version of the tune and a version illustrating how Corelli would have improvised off of this. Geminiani's information is quite accurate since he personally studied with Corelli. In addition, Geminiani also published several treatises, "A Treatise on Good Taste in Music" and a tutor for the violin that illustrate how to improvise ornaments and graces using the proper Classical method of fashionable improvisation.

Regarding the flattened bridge: this is simply a continuation of the Baroque bridge construction rather than trying to facilitate playing double stops. Baroque bridges were much flatter and the bows were much shorter documenting how Classical approach influenced and shaped fiddling traditions and styles. The popular eighteenth-century bowed was borrowed from the Lullian tradition of violin playing that emphasized short bow strokes, and a rhythmic approach to bowing echoed in contemporary fiddling bowing. Baroque and Classical classical violin techniques also emphasized the use of open string instead of the fourth finger because the gut strings in use at the time maintained a more uniform sound that did not ring as in modern steel strings.

The argument can never be resolved because people confuse a post Romantic approach to violin technique with the classical style of playing that shaped modern fiddling. Fiddling simply preserved older classical techniques while classical playing evolved to meet the increasing demands of larger performance spaces and virtuosic playing style incompatible with the older techniques found in fiddling. In short:

A violin has strings, and a fiddle has "strahngs". Have fun!!!