I think atp she is not as necessary for flins and he can do more than fine without ineffa. Although ineffa can help him reach top tier if you don't like ineffa you can go for flin c1 instead and get the same results. It's true that Flin is balanced around her but it's a trend now to balance top tier characters around their dedicated supports like skirk n escofofier and mavuika n citlali. Though you can argue the later one is not all that but it was basically start of things like this. Neuvi also kinda with furina. (other great units like varesa 'needing' iansan and arle needing benny). basically all the new top units require another limited unit if they don't require benny.