I tested them both and and I could only see TWO major differences...
1 - The Komplete Audio 2 is made of plastic whereas Focusrite's audio interfaces are made of aluminium. If you're cautious with your gear, you don't have to care... but if you're not, go for the aluminium.
2 - The software they are delivered with. With NI Komplete Audio 2, you may get lucky and have a promotion (free Guitar Rig 5 or iZotope Elements Suite). Personally, I don't mind the rest (Ableton Live 10 Lite, Machine Essentials, Monark, Replica, Phasis, Solid Bus Comp...maybe you'll do !). On the other hand, Focusrite Scarlett comes with XLN Audio Addictive Keys which are AMAZING (and XLN Audio Addictive Drums 2: Studio Rock is pretty nice as well).
So pick a team, and stick to it : plastic or aluminium ? Guitar-oriented and mix plugins or keyboard & drums VST ?
Considering your answers, you might want either one or the other. Otherwise, I have no complains : NI Komplete Audio 2 never failed me in 3 years.