I don't accept there was institutional discrimination.The likes of Maurice Hayes reached the highest echelons of the Civil Service.I think in the heavy industries in Belfast Catholics were intimidated by Protestant workers,and Management may have been negligent in not tackling this.
In any event you have to look at what motivated Protestant/unionists.Northern Catholics never at any stage showed allegiance to the Northern state,and this led to Protestant/Unionist mistrust which manifested itself in exclusion.I am not saying Catholics were right or wrong not to show allegiance to the Northern statelet,but undoubtedly this did contribute to Unionist mistrust,from which exclusion and some discrimination ensued. Paisley often referred to the lack of catholic support for and loyalty to the new Northern statelet and contrasted this with Protestant support for or at least willingness to co operate in the new independent state in the South from those Protestants who lived there.