I would not get too hooked up on the 1 joint definition. The workout plan I have mixed together looks like that mainly because I have been doing certain exercises for months. Surely one of the most beneficial exercise for you whole back would be deadlifts as compound move, but I am sick and tired of it for the moment
Also I mixed in hyperextensions since they benefit you if you work a lot sitting and I wanted at least one of the 4 to work the lower back, but not more. From the essence of 5x5 as described in the article hyperextensions do not fit in since they do not work the same muscle but focus on the lower back, but I just don't care. If you do not have a workout buddy try good mornings with heavy weight but be careful about your form.
Take "Straight arm lat pulldown on cable cross". You only move around one joint..the shoulder. But you have to keep your core steady, if you do not cheat leaning a bit forward, put a lot of tension on your lower arms, even a bit triceps to keep then straight and I definitely had to flex the chest as well as the triceps to keep straight with all the weight. It did work out the upper portion of the back, but also frontal shoulder and the other parts mentioned had to help as well. To me personally this makes it quite effective not just working one part, even though it is only 1 joint, you see where I am going with this. Wide reverse pull downs is using 2 joints but I could feel the strain on the lat more specific than anywhere else following muchmorethanmuscle's advise from another post to imagine the shoulders being stringed up..and definitely not the shoulder or the biceps that much. So I think some exercises work more efficient utilizing different muscles with more strain than others regardless of the 1 joint 2 joint thing. If you really find 2 exercises that you can perform fast as superset and you like how they work you, I do not think it is the end of the world to ignore the compound/isolation rule once..
As for "How is standing barbell curls a compound exercise?"
I am not seeing that one so much either, BUT If you do not cheat and do a clean exercise you definitly need your core and chest and upper back to stabilize yourself vs sitting using a scott machine though.you can try this one on gravity plate that has a ball in the middle, you will do the most perfect curls or else you will fall off
A good compound move would be rowing with the barbell bent over forward and supinated grip for example. Turning the pinky gives you a higher tension in your biceps but does not make the movement really that much of a compound move imo.
these are just my 2 cents its not like I am trainer or pro or anything remotely close...
I will post my arm plan later if there is interest.