I worked out EXACTLY how UNF determines its difficulty (developers I hope you change this), it takes the Page Authority of ONLY the #1 result - might as well just randomly generate a number 1 - 5.
If you want to determine competition easily on mass, use UNF + MS. Find 10k+ keywords, stick them in MS, analyse competition, untick everything except the majesticSEO stuff and in a few second you'll have a massive list of numbers, export it to excel, and sort the table smallest to largest. GENERALLY speaking the one with less results is going to be easier. From here you can analyse them one by one.
I've done a TON of testing to find correlations of difficulty metrics, and this is the only method that has some kind of correlation on a large scale (5000+ at a time). It is by NO means guaranteed at all.